Sometimes a word that really means "No" is needed, but the actual word "no" isn't available for one reason or another. A "safe word" can be aimed at the person who interacts with you, to underscore that you really need to hit the emergency brake. Or it could be meant for a third party that might come to your aid. Or both.
In the American BDSM subculture, three safe words are widespread: Red for full stop emergency shutdown, yellow for "This is too hard, I need us to slow down," and green for "Don't mind my screams, you can push harder." Some communities/cultures add "beige" for "I'm bored, get to it already!" (usually seen as Tempting Fate). Other countries' BDSM scenes can be considerably more lax, though, with some even forgoing safewords altogether and placing the responsibility on the dom to ensure that things don't get out of hand. Sometimes, such as when the bottom is gagged or may have difficulty verbalizing under stress, a setup is employed where the bottom holds an object that will make a noticeable noise when dropped and drops it as their safe "word".
Of course, any word can be used as a safe word. And the concept is not limited to sexual situations either. Commonly used by undercover operatives of all kinds while wearing a wire or being in a bugged room, people engaged in a combat sport, and people engaged in a setting where reality and fiction could easily be mixed up. (See Covert Distress Code.)
When Played for Drama, (sub)cultural flavor or similar, the safe word is likely to be either "red" or some other simple word that isn't easily used by mistake. When Played for Laughs, it is instead likely to be:
- Something hilariously unsexy, such as the name of an Ugly Politician Local to Area Where Writer Lives.
- Something which can be confused easily with something else, leading to hilarious consequences when the safe word is invoked by mistake.
- Something which is hard to remember or hard to pronounce, giving the character a really hard time.
No sexual or sexualized Real Life Examples Please. Non-sexual examples are okay.
- Mobile Suit Gundam SEED Destiny has a version of this that is both extreme and stupid. The Earth Alliance's enhanced soldiers each possess a "block word" that's supposed to render them docile. What it actually does, however, is drive them completely nuts. To make matters worse, the two block words we hear are common words that one is very likely to hear on a daily basis: "die" for Stella and "mother" for Auel. In fact, the one time we see Auel subjected to his block word, he blurts out "Mother's gonna die!", which in turn sets Stella off and makes the situation that much worse.
- According to Word of God, Sting's block word (the one that wasn't revealed in the show) is "dream", which is just as poor a choice as his teammates'.
- Indirect in City of Dreams: Those who don't want to play anymore simply wake up.
- A Buffy the Vampire Slayer fanfic has the safe word Hellmouth, chosen for its unsexyness.
- A Harry Potter song-fic for Rihanna's S&M, were the safe word, and title, was Skittles.
- In the Iron Man fanfic, "A Kink in the Armor", Tony and Pepper use 'board meeting' as a safe word.
- In the House fic "Immobile" House and Wilson's safe word is "lupus".
- In the Marvel Cinematic Universe fanfic, "The Watcher Watched", Tony Stark and Loki enter a secret BDSM relationship. In chapter 5, they started to use a safe word. Loki's safe word is Jotunheim and Tony mentioned that he used buttercup in his past relationships.
- The NCIS fic "Shards To a Whole" combines this trope with "You Called Me "X"; It Must Be Serious"; Since Tim McGee and Abby Scuito seldom call each other by their full names, Tim's safe word is "Abigail" while Abby's safe word is "Timothy".
- Averted in the Maleficent fanfic Your servant, Mistress: Diaval asks to be given a safeword, Maleficent tells him that his safeword is "no", or any other indication that he wants to stop - she isn't into rape-play and thus sees no need for a safeword. She offers him that he can choose one if that makes him feel better, though.
- In the third Ice Age film, Manny and Ellie choose "Peaches" as the code word for if Ellie goes into labor while they're down in the world of the dinosaurs (which she does, though she and the baby are ultimately safe). They end up naming their baby (who turns out to be a girl) "Peaches," so it turns into a Meaningful Name.
- The Jungle Book (1967): The elephants will only stop marching when they hear the word "halt" rather than "stop", something that Bagheera manages to figure out.
- EuroTrip features a combination of confusion and hard to remember when Cooper unknowingly goes into a BDSM club, Vandersexxx. The safe word in question? "Flüggåɘnk∂čhißøl∫ên." Yes, thats the Euro symbol, a partial derivative sign (∂), and an integration sign in there.
- When Cooper finally thinks he's gotten it right and says "Yes, for the love of God, Flugenkempfheimler," it turns out the Flugenkempfheimler is a particularly bizarre Noodle Implement. With a laser sight and feather.
- Four Christmases: The main characters are visiting the parents. They decide to use the word "mistletoe" for when they cannot take it any longer and want an excuse to leave.
- The Goods: Live Hard, Sell Hard has one character, after being bored with "making love," tells the girl he is with to do whatever she wants. His safe word is "Blueberry Pancakes."
- Invoked in Serenity: the phrase that puts River to sleep ("Eto kuram na smekh!") is referred to as one of these. Strangely, it's a popular Russian idiom that wouldn't make for a good code phrase in Real Life (it literally translates to "it's for chickens to laugh at" and means "it's ridiculous"). There must be no Russian speakers at all in this system.
- Hot Rod: Rod chooses the word "whiskey" for his safe word when practicing for the big stunt at the end of the film. Unfortunately, not only can he not pronounce the word correctly, but his crew is unable to help him anyway.
- Bound (2015) uses the traditional safeword of "Red" in exactly one place, the alley-way, with no prior or subsequent explanation.
- In Deadpool, Wade, as he's being strapped to an examination table in Ajax's laboratory, suggests "Pork N Beans" as a safe word.
- Callahan's Crosstime Saloon (Callahan's Lady):
- Played with by Spider Robinson. In the Bower at Lady Sally's (a pretty much anything-goes orgy room), there's only one safeword: "No". Also, Lady Sally's artists have a code word they can use to call for help if a client gets out of hand (the rooms are all on audiotape which is constantly monitored).
- In the later book Lady Slings the Booze, one of Lady Sally's employees explains the concept of safewords to an outsider. They use two: "the First Word" (called Yellow in the trope description) and "the Second Word" (Red).
- Kushiel's Legacy: A safe word is known as a signale. To persist with BDSM play after a partner has given the signale is considered heresy according to their religion of "Love as Thou Wilt."
- The Last Hot Time: Appears in this story by John M. Ford, as the hero learns about BDSM.
- A Strong Hand: In Catt Ford's story, the main couple use the safe words "London" (for stop) and "yellow" (for slow down).
- These Words Are True and Faithful: Ernie says to Sam, You really are new at this, arent you? You dont even have a safeword, do you? Sam later picks a safeword but never uses it.
- Ties That Bind: This is one of the topics Guy Baldwin discusses in this book.
- The Administration Series: While relaxing in the Sim, Warrick sees a moving plastic duck that a programmer had left. Later that evening, during a BDSM/sex session with his one-night stand, the first safeword that comes to his mind is "plastic duck".
- The standard "red" for "stop" and "yellow" for "slow down" are established in Chapter 11 of Fifty Shades of Grey, and it is implied that Ana could have stopped any sex that happened or was threatened after that point. However, the next two books establish very clearly that whatever Ana does regarding safewords, she's going to be wrong. At the end of Fifty Shades Grey, Ana asks Grey to beat her as hard as he can to see if she can handle it. She hates it and leaves him because she can't deal with being hit that way. In Fifty Shades Darker, however, he says that they both behaved stupidly, demanding to know why she didn't safeword—never mind that she was testing his control and her own endurance, or that safewords had never been defined or explained to her. Several months later, in Fifty Shades Freed, Grey is torturing Ana with orgasm denial while she is shackled to a piece of bondage furniture; this is quite literally revenge for her not being home when a kidnapper (and attempted rapist) arrived at the penthouse. Ana, for the first time in three books, screams, "Red!" Grey equates her safewording with someone attempting to kidnap her. Both, to him, are equally upsetting:
"A deranged asshole gets into my apartment to kidnap my wife. She won't do as she's told. She drives me crazy. She safe words on me."
- The Patchwork Girl. The protagonist (who is from a Free-Love Future Earth) is about to have sex with a Fair Cop from Luna, whose society is sexually conservative. Knowing that she's nervous, he gives her a safeword which she can use to make him stop at any time: halogens (then he quips, "And then you have to list them.")
- The Office (US): Michael becomes Jan's partner for a period in the third season, but is unnerved by her many fetishes and fondness for roleplay. But he's too much of a wimp to leave her, even when she "forgets" their safe word. Luckily he manages to by the end of the episode.
- Tracy on 30 Rock: "Boundaries are made to be tested. That's why my wife and I stopped using a safe word."
- On CSI: Miami, an undercover agent indirectly causes the death of a woman he was using to collect evidence on a drug dealer when he ignores her (coded) call for help.
- In the original CSI, Grissom and Lady Heather are having an academic discussion the concept of the safe word in BSDM context, (in a scene rife with Unresolved Sexual Tension), specifically the idea that the dominant must respect requests to stop. Several episodes later the discussion receives a dramatic Call-Back - Lady Heather has caught and chained the man who tortured and killed her daughter and, in a rage, is whipping him bloody, and only stops when Grissom invokes the rule and forces her to acknowledge it.
- Finn's safe word? "Stop".
- In one of the first "I'm Carol" sketches on Saturday Night Live, Carol was at a BDSM party where they went through everybody's safe words twice because Carol couldn't remember what they were. 
- Another SNL BDSM sketch, involving Kristin Wiig as politician Nancy Pelosi, ended with the sound of a belt sander as a dude is screaming. She runs off stage yelling the safe word. For the record, it was "Palomino".
- In White Collar, Neal has to go undercover with minimal surveillance (GPS and audio) to determine whether his target has some stolen bonds. His code for the FBI to move in is "long flight".
- Peter and Elizabeth have "azaleas," which lets Elizabeth know if Peter's all right if he's in a potentially dangerous situation. Mozzie's is "bread basket".
- A similar thing in an episode of Mad About You, when Jamie ropes Paul into making a new "I ♥ NY" commercial. They talked about having a code word, like "paramecium" or "Estes Kefauver", but never actually settled on one. Then they were on the set, and by now it's way too late to back out:
Paul: Honey? Paramecium! Big ones!
- On The Drew Carey Show, when Drew & Co. went to visit his creepy stalker (but discovered that the stalker had modeled his house, and his life, after Drew's) the signal was for someone to say he was tired. After the stalker takes them prisoner, Oswald says, "Boy, I sure am sleepy," as if that would get them out of their predicament.
- In The Pretender, a simulation could be interrupted with the safe word "Refuge".
- In Castle, Castle has the safe word "apples", used in two episodes so far - in fact, he mentions it the very first time that Beckett handcuffs him i.e. the pilot, demonstrating his Chivalrous Pervert side. There are also hints that Beckett has a dominant streak.
- In Gene Simmons Family Jewels, Gene had to experience some domination and had the safe word, "ice cream".
- Non-sexual example from Sabrina the Teenage Witch. Sabrina and her friends are going to a party, and are afraid it will be boring. They agree to use "Kazoo" as code for "Get me out of here!"
- Important Things with Demetri Martin had a series of skits about a BSDM couple that had chosen unfortunate safewords, one of which was "the correct pronunciation of Gnocchi." In the second skit the Safe Word was "Bill Paxton," only the Sub couldn't remember his name ("AGH! That...that guy! He was in that movie! AGH!"). The last sketch of the episode features them looking up 'gnocchi' in the dictionary and arguing about it.
- On Desperate Housewives when Rex is teaching Bree the basics of domination, she immediately requests they change the safeword, as it happens to be the city her aunts lives in and doesn't want to think of her aunt during sex.
- Barney and Robin from How I Met Your Mother use "flugelhorn."
- In one Law & Order: Special Victims Unit episode, the detectives interview a woman who sold the Victim of the Week some BDSM sex toys as they investigate whether the death might have been caused by a sexual accident rather than murder. She's upset at hearing about the victim's death, explaining that she taught her about code words and safety. (Minutes later, the detectives find half a million dollars' worth of diamonds inside the handle of an unused whip, and the investigation is redirected to high finance crimes.)
- Discussed on Buffy the Vampire Slayer. After Angel prevents Faith from raping and killing Xander, she briefly tries to suggest that they were role-playing. His sarcastic reply is to ask if Xander forgot the safe word. Faith's response is "Safewords are for wimps".
- Non-sexual example: Frasier and Roz agree on one to let Roz know if Frasier's not interested in a blind date. It takes less than a minute for him to use it.
- In an early Portlandia episode, Fred and Carrie crossdress as a couple who use "cacao." It gets out of hand, to the point where female!Fred texts "cacao" to male!Carrie when they're on opposite sides of town.
- Louis in Suits: "Safewords are for pussies." (Warning: In real life, this is bad BDSM practise and can lead to unintended sexual assault, safe words are important.)
- When Bo has a rebound threesome in the Lost Girl episode "Faetal Attraction", she comments "We're going to need a safe word." The episode fades to black before we find out what the safe word actually is, though...
- Non-Sexual example: In an episode of Psych, Jules must go undercover on a dating website to help catch a serial killer. While on the dates, she uses 'I'm hot' to indicate that she's in trouble and 'I'm cold' to indicate that everything's okay.
- The British comedy series Safeword uses this as a premise - two guests pick safewords at the beginning of the episode and use it when the tasks (allowing comedians access to your social networking accounts, insult-fests) become too embarrassing for them. For example, Sinnita used 'Brad Nip' (turns out they dated in the late 80's - who knew?)
- Early on in the American Queer as Folk, Michael gets drawn into a night out at a sports bar with the female coworker who's crushing on him (and whom he's letting crush on him as a cover at work) and another, very straight/homophobic coworker and her husband. He and Brian joke beforehand about having a safe word ("buttplug") for when the night gets to be intolerable. Crammed into a booth with a beard he likes and loud homophobes he doesn't, trying to pretend to be straight, Michael is so miserable he ends up muttering "buttplug" to himself within minutes of his arrival, and on taking a call from Brian (turning around in the booth and leaning out the back of it, which apparently allows him not to be heard) immediately starts with, "BUTTPLUG BUTTPLUG BUTTPLUG!"
- Saints Row: The Third has a brothel named Safe Word, a club for those with BDSM tastes. Kinzie mentions hers is "teacup" and she is quickly spirited away before she can reveal more bits of information. In Saints Row IV, a recreated AI Tanya tells Kinzie she'd make a good addition to her brothel, Kinzie quickly cries out "Teacup!"
- A Sidequest in Dishonored involves messing with an art dealer strapped into an electric chair, using it for masochistic play. His safe word? "Retribution." Corvo can choose to ignore it and shock him until he passes out.
- At the beginning of Magicka, the player character(s) are accidentally dropped into a dungeon where the tutorial takes place. Someone from the party above shouts down, "Remember, the safe word is 'Banana!'" The pause menu will have an option simply labeled "Banana," which allows you to skip the tutorial.
- In Dragon Age: Inquisition, when romancing The Iron Bull he sets up a few ground rules due to the dom/sub dynamic present in the bedroom and the massive size differences between you two, one of which is using "Katoh" as your safeword. Later on, he can even talk about what he thinks the other companions might use as their own safewords. He also gives a very good reason why certain safe words are better than others and why it should be something you would never say otherwise, as it can be said by accident and cause confusion for your partner.
- Mockingly referenced in Payday 2 with one of the taunts from the Cloaker enemy when he gives you a No-Holds-Barred Beatdown being:
Cloaker: Alright, the safe word is Police Brutality.
- In a subversion, Uncharted 4 shows protagonist Nathan Drake on the wrong end of a serious beatdown from mercenary antagonist Nadine. He starts yelling 'Mango!' over and over.
Nate: Mango! MANGO!Nadine: What are you on about?Nate: That's my safe word.
- In the pre-fight banter cutscenes in Injustice 2, when an opponent makes a particularly vicious or Double Entendre-laden threat to Deadpan Snarker Green Arrow, he may reply with, "My safeword is 'Arrow Cave'."
- The adult otome game The Confectionary has the monster, ahem, companions each have their own personalized safe words; "rawhide" for Cinnamon, "headshy" for Sweets, "drought" for Black Pudding, "heartscale" for Jawbreaker, and so on.
- In the BDSM-heavy Blood Bank, the protagonist and his love interest use "rose" as a safe word both inside and outside the bedroom.
- Prominently referenced and sometimes used in Collar 6, seeing how it is all about BDSM. Laura's safe word, for example, is "halo".
- Cyanide & Happiness gives us what might be the most ill-chosen safeword ever.
- Saturday Morning Breakfast Cereal teaches us that introducing safewords in nonsexual contexts is a fun way of creeping people out.
- Subverted in one Something*Positive strip, where dominatrix Candy comments on a heartwarming moment and her client says "How sweet!" Then...
Client: "How sweet" is my safeword, mistress!Candy: Well not any more! Guess the new one!
- The BDSM webcomic Sunstone is named for Ally's safeword, which both of her subs Lisa and Anne use when they're with her. Alan's safeword, which Anne uses, is a three-note hum that can be used through a gag, though Marion's safeword with Alan was shown to be "mercy."
- A yoga variant in this Unshelved strip, in which the safe word is "Ow!"
- xkcd teaches us chemists have the worst safewords, being way too long to say before things start hurting..
- Marvel/DC: Apparently, Gobby's safe word is "pumpkin."
- In Tales of MU, Mackenzie's safe word is "basement".
- The live chat audience of online web show What the Fuck Is Wrong with You? has a safe word; "purple shotgun" which is usually reserved for co-host Tara's childhood horror stories. It doesn't do anything.
- In the Bum Reviews 50 Shades episode, Chester's safe word is "change" when he's being dominated for money.
- Though it was set up for a sexual situation, the safeword 'broccoli' is used in Storm of Souls to instead get the badly injured main character to calm down and stop moving so he doesn't reopen his wounds.
- In the Dragon Ball Z Abridged adaptation of Dragon Ball Z: Broly The Legendary Super Saiyan, the Shamoshans (the tiny aliens forced to build "New Planet Vegeta") were recast as extreme masochists who went along with Paragus' plans because they enjoy being dominated by stronger beings. They even come to watch the heroes fight Broly because of how violent it's going to be — however, even they have standards, and when Broly says he's going to blow up the planet they hurriedly try to recall their safeword. It turns out to be "broccoli", which the elder Shamoshan tearfully laments was "lost to time".
- Ultra Fast Pony: In UFP The Movie: The Moviening, Rarity gets really excited at the prospect of all her friends wearing her kinky horse costumes, and gleefully mentions that the safe word is "Keep going."
- In Family Guy, Peter and Lois use "banana" as the safe word when they do BDSM.
- In Team America: World Police, our hero has a safe word when playing with the terrorists, so that his friends will know when to pull him out. Because of the kind of movie this is, of course it doesn't work!
- Even better, it's less a safe word and more a "Safe Wild-Waving-Thrashing Gesture." Which makes it even more hilarious when it doesn't work, despite the sign being really, incredibly obvious.
- In the Superjail! episode "Cold-Blooded", Jared is sent into the prison undercover (against his will). The warden tells him that if things get rough, he can just say the safe word and Jailbot will get him out of there. Hearing that the safe word is "Baby make weewee," Jared objects that it isn't a word, much to the Warden's annoyance. He then uses it almost immediately, but since the twins messed up Jailbot's circuitry, he's out of luck.
- The Simpsons:
- There is a non-sexual version in "Large Marge", where Bart's old elephant Stampy will flop on his side and become docile when he hears the word "Mugumbo". He uses this as part of a plan to restore Krusty's reputation, but he forgets the word at the key moment and doesn't remember it until Marge flashes her surgically-enhanced breasts at a trade show audience, causing him to cry out "Check out those mugumbos!"
- In a parody of Paranormal Activity, Homer has to accept the deal with a demon: in exchange for not taking Maggie away, he must get into a threesome with him and another demon, with the safeword being "cinnamon". Later, when Homer covers the camera and expresses his desire of trying something new, we hear the demon screaming "Cinnamon! Cinnamon!"