These are extras that hardly ever interact with the main characters, even though logically they ought to do just that.
For instance, a Cop Show might focus on six cops who are often seen doing their jobs at a police station. Lots of other cops and staffers walk around, carrying papers or whatever, but none of these other people actually talks to or interacts with the main characters. Nor do they talk to each other, at least not in a way that the audience can really see. They're just filling out the background, making the police station seem more realistic.
There are practical reasons for this trope. If the extras start talking to the main characters, then the extras themselves will become characters. This will require higher wages and proper crediting. Besides that, the writers might not want to bother keeping track of so many extra names and faces, or they might not want to make the audience bother.
Sometimes a Ghost Extra will get promoted and become a proper character. This is a nice trick for the writers, because they don't have to explain where the new character came from; they can just say she was "there all along" but nobody previously talked to her on camera.
Often paired with The Main Characters Do Everything, if the main characters are part of some larger group.
- A Taco Bell ad shows three characters having a discussion about the new "Queso Crunch Wrap" in the middle of an elevator... while the rest of the occupants ignore the three and move their lips to each other without any noise actually being made by them.
- In New X-Men Vol. 2, Academy X and New X-Men, there are a number of 'extra' students seen walking in the halls that never speak with the cast or take any notice of any of the things going on in the school. They don't even appear on the squads every student was theoretically part of.
- In The Empire Strikes Back, the Imperial crewmen and technicians aboard Darth Vader's flagship rarely get any lines. However, the camera frequently focuses on them to show just how terrified they are as the Sith Lord is strolling along the command deck.
- Phule's Company features a heavily armed force of 200... barely a dozen of whom have names.
- This happens throughout the Harry Potter series, mainly in regards to how many students there are in Hogwarts. While there are plenty of them who are secondary characters, there are still plenty of mentions of random students milling around in the dormitories or Great Hall, who never interact with Harry.
- This would be Truth in Television for a typical Good Old British Comp of the sort that JK Rowling attended, where a student body of fifteen hundred isn't unusual and class sizes tend to be in the region of twenty-five to thirty; you couldn't possibly interact with more than a fraction of your own yeargroup, much less the whole school. It makes rather less sense when you consider that the population of the Wizarding World is supposed to be quite small; estimates vary, but most people estimate the Hogwarts student body at a couple of hundred at most. The fandom has wept blood trying to make sense of it all, and it's probably best to apply the MST3K Mantra.
- The Bill was a particularly conspicuous offender. The cast of regular characters numbered around 20 or so, but beyond those we also seen hundreds of others who would always be milling about in the background, etc. The area where this trope comes into full effect it that sometimes they literally did come across as being ghost extras, where we would see the regulars walk around them in corridor shots almost as if they aren't even there at all. Sometimes a "ghost extra" would hold open a door for a regular character, but you'd almost never see the regular thank them...
- CSI (various). It is almost as if the main characters and the extras are in completely separate worlds. Sometimes the main characters have dramatic arguments and yell when they make a sudden discovery in the lab, but all the extras just ignore it completely, not even giving them so much as a funny look. Furthermore, all cases require the expertise of people from the main cast and only people from the main cast.
- Stargate Atlantis has an episode where Sheppard is told, loudly and over the radio so that everyone can hear it, that something important and dramatic has happened in the control room. He immediately jumps up and runs out of the room while all the extras just stand there.
- Dexter features a large police station, but every case ends up being investigated by members of the regular cast - Doakes gets magically paired off with Batista when La Guerta isn't there to be his partner, even though there are presumably many more police officers available.
- NCIS: Has this trope bad. None of the other agents seem to do anything but die. Lampshaded in a parody fanfic.
"The man was dragged off by a member of another team, who Tony suddenly realized he had never seen before."
- Played with by Lost: while the show has kept a relatively stable slate of extras, and given many of them names and brief interactions, they never actually get to do anything (except help out in day to day survival in the background and get killed.) Even when this is lampshaded, it's done with new actors who've never been seen before, as with Arzt, Nikki, and Paolo.
- Occasionally subverted on Battlestar Galactica (2003), as when Gaeta gets angry and the entire bridge stares at him. In the Razor DVD commentary, Ron Moore talks about the difficulties they had with union rules for the scene where all the cast and extras chant "So say we all!" During the build up to The Mutiny they made a point of showing the extras reacting to conversations between the main cast, which were also shown to be intended by one of the participants to be heard by those extras.
- Corner Gas had several extras, but all they ever seemed to do was mill around in the gas station or the Ruby. One notable extra was Lacey's cook/busboy Josh, who never spoke...that is, until an episode in which he got angry and quit, telling Lacey that she never cared about him or even seemed to notice him. He's a real person with real feelings, dammit, and she doesn't even know that he's always dreamed of becoming a llama farmer!
Lacey: [angrily yelling after Josh] Yeah? well, be careful! They bite your fingers off!
Brent: Oh, that's not gonna work. Danger's part of the allure of llama farming.
Lacey: Did you know he wanted to work with llamas?
Brent: I didn't even know he could talk.
- In an episode of Murphy Brown, we finally get to meet some of the crew when one of them, Jack, passes away and leaves a will that asks his dear friend Murphy to read his eulogy and handle his posthumous arrangements. Murphy doesn't remember him at all, and spends the entire episode feeling guilty that this man who considered them to be so close doesn't register in her mind at all. It turns out Jack does not exist. The crew made him up in order to show Murphy how she didn't treat them like they were real people. It works on the audience, too, because as far as we've seen so far, they're only this trope.
- Star Trek: The Next Generation: This is common in the series, as Enterprise crewmembers are routinely mute while doing their duty. Just think of every time a scene begins with a main character giving a redshirt an order, and said redshirt just slinking away silently, or whenever a main character comes to replace a redshirt who was filling in for him or her on the bridge. And speaking of the bridge, the camera rarely focuses on the aft stations or the extras manning them (who may as well just be playing Pac-Man).
- Star Trek: Voyager has a small Federation ship stuck at the far end of the galaxy (and even then, they find five more). The producers do deserve credit for having consistent background folks throughout all seven seasons. Though if an Ensign starts having actual speaking lines, you might want to look for something to duck behind - many redshirts do get to speak lines and kick ass and then melt back into the background relatively unscathed like a future version of Batman. What particularly lampshaded this was the odd episode in which a crewmember would be important to the plot of the episode, and the regulars react as if they all know him.
- Star Trek: Enterprise took this to the extreme, lacking any B-Cast for the first two seasons. Aside from the dozen people silently milling about in engineering, the other members of the 80+ crew were conspicuously absent at all times.
- Star Trek: The Original Series averted this, probably thanks to their Recurring Extras: background characters can often be seen reacting to events (e.g.: looking around with amusement when Kirk sits on a Tribble). Fan favorite episode "The Doomsday Machine" used this to great effect. The director took the extras and had them visible in every scene and watching the main characters. A major part of the episode came down to main and guest characters pulling rank and debating command protocol while facing off against a particularly powerful planet killer machine. It went a long way to show that even though they didn't have any lines, they had opinions of the situation. This climaxes with Spock just needing to wave his hand for the Bridge's security guards to eagerly step forward and wait for the officer to give the word for them to drag out the Commodore before his Moby Schtick kills them all.
- Played with on Oz, wherein the background prisoners rarely changed, but also rarely spoke...until a plotline centered around a group they were a part of, such as the Latinos or Gays. At some point, all of them got their time in the sun, which is pretty impressive for a series with such a large cast and so few episodes per season.
- Played with in Degrassi Junior High: Cast members would be played by "The PWT Repertory Company", with only the speaking members being credited in the episode. The idea was that each kid would get A Day in the Limelight, with a Story Arc playing in the background and a comedy subplot featuring Arthur and Yick. Probably didn't quite pan out the way the creators intended, but they made a rather game attempt.
- The Musketeers: You'd be forgiven for thinking that the main four characters (plus the captain) made up the entire Musketeer regiment. The others can be glimpsed around the barracks and occasionally acting as silent backup, but the main characters never interact with them and they all seem to have exactly the same long-haired design.
- Babylon 5 definitely has a good few of these. However, they also subvert/avert it, by making sure to give the extras more to do, and having at least one extra Opt Out at the Line in the Sand. Generally, the extras also do at least react to stuff, including the rather nice scene where Lyta demonstrates her psychic powers.
- Joshua Cox, as Lt. Corwin, started as an extra, then got lines, then became a character. His Slavic C and C colleague was not so lucky.
- Taxi had a full complement of drivers beyond the half-dozen-or-so actual characters. Once in a very great while, you might see one of them respond to a cab assignment from Louie, but other than that...
- In Frasier, the main characters frequently sit in the same coffee house ("Café Nervosa"), and Frasier and Niles especially seem to be visiting it almost daily for years, yet they never seem to be familiar with any of the other customers. Whenever a minor character is introduced by having a main character meet him/her at Nervosa, it's always someone they've never seen before. Apparently Frasier, Niles, Martin, Roz, and Daphne are the only regular customers Nervosa has. This is especially odd considering that Martin's regular pub, "McGinty's", is depicted as a place where everybody knows your name. Admittedly there's a difference between a pub and a coffee house, but still.
- Similarly, KACL, the radio station which employs Frasier and Roz, is shown to have plenty of hosts and other staff, but most of the time Frasier and Roz only interact with a handful of them.
- On Boy Meets World, the other students in the main characters' classes often seemed to be in a whole different place altogether. They never really interacted with Cory, Shawn or Topanga or reacted much when one of those three made a scene in class, and the teachers (Mr. Feeny or Mr. Turner) would only call on Cory, Shawn or Topanga in class and were never seen talking with the other students. The latter point was lampshaded in the series finale:
Mr. Feeny: I regard all my students equally.Shawn: You know we're your favorites.Cory: Come on Feeny, you haven't even talked to another student for seven years.
- Sequel Series Girl Meets World continues this tradition in its first season (where it's much more noticeable because the four main students constantly speak up in class, often derailing Cory's lectures in the process), but surprisingly averts it in the second - in "Girl Meets the Secret of Life", a minor character named Yogi (an extra who appeared throughout the first season, but didn't have a single line) speaks up to make a point that even though he isn't Cory's daughter, the events in his life have significance to him and aren't meaningless. Surprisingly, this isn't just a one-off gag - Yogi has had lines in subsequent episodes.
- Friends, most of the time. This was lampshaded occasionally.
- In Life On Mars and Ashes to Ashes both homicide rooms were populated by ghost extras (quite ironic in retrospect), as well as the main cast. At one point, Sam Tyler, who believes he's dreaming, suggests he's going to keep on walking until he runs out of faces.
- M*A*S*H. It's strongly implied in the first season there are more doctors in the camp than just the main cast. Every time a show's plot revolves around nurse interaction (specifically in the episode 'The Nurses'), several new actresses are cast and the show's regular background nurses are ignored. Klinger is often seen performing corpsman duty as well as cooking, maintenance, day and night sentry, garbage duty, and eventually clerk duty, despite the fact there are several dozen men walking around in the background doing mostly nothing. Members of the main cast are occasionally found working the bar at the officers club when they very clearly have more important responsibilities elsewhere.
- This is also the case on JAG. There are many people in the bullpen but they rarely ever interact with speaking characters. It gets particularly obvious that every staff meeting only includes lead and recurring characters, and sometimes also the guest star.
- Holby City zig-zags this trope by giving them some dialogue and interaction, but they are never credited in the Closing Credits.
- Averted almost constantly in the Disney Channel Italia show Game On! The main characters are the ones with the most clout and skill/experience in Sunomy (or have some connection to these characters, like the ones who run the building cafe), but the extras are still seen working in the background and occasionally even seen talking and working indistinctly with the main characters when the focus isn't on them. There are a number of moments where a silent extra's interactions with the main character are a pivotal point of the scene or a joke. In fact, many of the extras noticeably reappear multiple times for episode after episode and join the main characters in activities. Sometimes it seems like the biggest difference between main characters and extras is that the extras don't have distinct scripted lines.
- Every background person in Under the Dome is in exactly the same predicament as the main characters — stranded in a Domed Hometown. They just go about their business, though, despite the fact that most people's jobs depend on people and resources going in and out of town - something that isn't happening.
- Frontier Circus had nameless extras who made the majority of the performers and crew of the T & T Circus, who generally milled around spectating while the regulars and guest stars dealt with that week's plot.
- This gets lampshaded multiple times in Victorious by the main cast, saying that their other classmates only react to stuff.
- This happens a lot on Will & Grace. One of the character will do or say something really outlandish in front of (or to!) a bystander. Since the bystander is an extra, with no dialogue, they will just mutely react. Sometimes, they won't even react.
- Stargate SG-1 has an awful lot of soldiers wandering around Stargate Command but never really interacting with the cast. Interestingly, most of these extras were in fact actual soldiers: the US Air Force approved quite strongly of the Stargate series and would frequently lend personnel to the show.
- The crew of the Normandy in Mass Effect is quite consistently there, but (for the most part) not interactive in any way. Their main purpose seems to be being in the line of fire, especially in Mass Effect 2. When they're all taken by the Collectors in the second game, EDI fills in for the entire crew without any problems. The only reason she wasn't already doing so was due to her Restraining Bolt, since Cerberus feared having an AI that could not be controlled.