"iBloop" alludes to Miranda Cosgrove's previous role as Megan in Drake & Josh by having Drake Bell randomly appear on set and address her as Megan, before asking where Josh & their parents were, and who Mrs. Benson was.
In "iGet Pranky", it is revealed that Carly has never pulled a practical joke. After being pressured by Sam and Freddie, she unsuccessfully attempts to prank Gibby. Later in the show, she's shown watching TV, and you can hear the final scene of the Drake & Josh episode "Megan's Revenge" when Megan (who is well-known for her pranking) causes an explosion that makes the floor under Drake and Josh collapse. Carly sighs, saying "How come that little girl is so good at pranking?"
In "iToe Fatcakes", Carly watches a Megan-centric scene of the Drake & Josh episode "The Peruvian Puff Pepper" before flipping to another channel.
Nathan Kress, who plays Carly's leading man, had a guest role in the aforementioned show where he hits on Megan (played by Cosgrove) to no avail. Dan Schneider liked his performance so much that Nathan's scene was cut from the episode and was immediately cast as the male lead for Miranda's new show, iCarly. Guess how Nathan's role began on the show.
In "iPilot", Carly watches an episode of Grey's Anatomy in which Nathan was a guest star; while that happens, Sam pulls Freddie from his legs into Carly's room.
The character of Sam Puckett is based off Jennette McCurdy's guest role in Zoey 101 where she also played Trisha Kirby, a very mean girl. While Trisha doesn't appear as violent as Sam, she is definitely as delinquent, lazy and precocious as Sam, and how pushy she comes off as and she also failed a grade. It could be said that she is a form of an Ascended Extra, except its a different show and character.
Jerry Trainor, who plays Carly's older brother Spencer, had various goldfish as pets, which seems to allude to this short film
Victoria Justice's guest star in "iFight Shelby Marx" is alluded to in "iParty With Victorious" when Sam points out Victoria Justice's character, Tori Vega's, similarity to Shelby Marx.
In "iParty with Victorious", Sam remarks that Marissa hadn't had a date since Seinfeld got cancelled, to which Marissa remarks, "It wasn't cancelled! Jerry chose not to do another season!" Mary Scheer (Marissa's actress) had 2 guest roles on Seinfeld.
Before the Season 5 'inversion' of the trope Nickelodeon aired this show multiple times a day, gave it and star Miranda Cosgrove extremely good treatment, more than any other Nickelodeon show that isn't Spongebob. Along with the many merchandise and magazine attention the show gets it was Nick's flagship show. The show was given an open cheque for renewal as long as the main trio wanted to continue doing it. They even got a fifth season, which is very rare for Nick or Disney shows.
The inversion happened after that 5th season. The Seddie arc tanked badly, and Nick decided to push Victorious as the best show on the network, dumping Miranda Cosgrove as the network star in favor of Victoria Justice and ceasing to promote episodes well, with some not getting any promotion at all.
Dawson Casting: Averted with the main cast. However, Griffin, Carly's love interest in "iDate A Bad Boy", was played by a 23-year-old and looked like it. The episode involved some heavy make out sessions with the star of the show Miranda Cosgrove, who was 15 when they filmed them. Miranda apparently got to choose which guy they casted.
In "iPsycho", the girl who keeps the trio hostage looks like a 22-year-old instead of a 16-year-old.
Played somewhat straight in the latter seasons. By "iGoodbye", Jennette McCurdy was 20, Miranda Cosgrove was 19, and Nathan Kress was 19, turning 20 just days before "iGoodbye" aired.
Some people who don't ship the Sam/Freddie relationship have called the the second half of Season 4 "iSeddie" or "iSam", due to the Seddie shipping arc taking up 4 out of the 9 episodes filmed and Sam and Freddie together continually taking the A-Plot with Carly pushed down to the B-plot or C-plot in pretty much every episode, especially as some episodes had Carly in a plot completely away from the rest of the main cast. Many consider it a Spinoff or Continuity Reboot instead of a new season with characters who look, sound and share the same names, but aren't the same characters from previous seasons.
Ironically, Sam was eventually given a spin-off show called Sam & Cat.
The imaginative, pejorative names of "Sucky" and "Cruddie" for Seddie and Creddie respectively.
Friday Night Death Slot: Despite most of the second half of Season 3 airing on Fridays (mostly while they still had more episodes to air and when Big Time Rush needed more publicity), it managed to avert this and still did pretty well in its slot most of the time, getting solid audiences there often. The "iSpace Out" special had over 5 million viewers even in the presence of a new episode of The Suite Life on Deck airing at the same time. And when "iGot a Hot Room" aired in the summer, it aired against another new episode of the same show and absolutely obliterated its ratings. However, "iStart a Fan War" didn't exactly stand out as well as one would have expected, scoring only 5.02 million viewers. Guess what screwed it over?
Harpo Does Something Funny: Most of the dialogue was retroscripted, with Dan Schneider sometimes feeding the actors new lines right before they did a take.
Lying Creator: The week before the "iSaved Your Life" episode aired, a promo aired showing Carly/Freddie kissing. Dan Schneider, in an effort to calm the shippers of the Sam/Freddie pairing, implied it might not be what it appeared. Cue the episode, where they ended up kissing 7 or 8 times, and it was as it appeared.
He posted a picture of Carly and Freddie kissing as a tease for "iSpeed Date"m then cut the kiss out later because of a kiss would have impacted on the story of "iSaved Your Life". The kiss was likely to have been removed from the script before filming because they would have done the 2nd script already, so he basically created a blatant piece of lying Ship Tease for no reason.
Not Screened for Critics: Like every teen and children's show, iCarly is not shown to critics. In combination with closed set filming and tight control on information being passed around, Dan managed to keep the Sam/Freddie plot in "iOMG" and every episode in the subsequent story arc a secret.
Periphery Demographic: Each season skewed older than the last as word got out among adults and the original target cohort grew up.
Playing Their Own Twin: In the episode "iTwins", Jennette McCurdy plays the roles of both Sam and Melanie Puckett, identical twins who are polar opposites. This is actually lampshaded throughout when Freddie is convinced Melanie is just Sam in disguise.
In-universe example: Gibby is a huge fan of the British boy band One Direction and got to sing with them as a ploy to get their lead singer to stop pretending to be sick so he could keep staying at Carly's and be nursed by her.
Real-Life Relative: Gibby (Noah Munck)'s brother Guppy is played by his real-life brother Ethan.
The sidewalk where Josh ran around in "Dinner With Bobo" is the same sidewalk Carly rode her electric-powered scooter in "iGo Nuclear".
The pathway in "The Wedding" where Drake and Josh got stranded in their car is also the spot "Somewhere Outside Tokyo" where Carly, Sam, and Freddie were ditched by Kyoko and Yuki in iGo To Japan.
Any big room needed ends up being a redress of the main iCarly studio set. Examples include Freddie's room from "iSaved Your Life". And probably Carly's room in "iGot A Hot Room".
The school hallway/locker area is a redress of the school set from That's So Raven, with the main difference being the addition of a central wide door entrance, and iCarly not using an extra part of the hallway on the right side of the entrance. The entire set itself began its life as the school hallway set on Saved by the Bell.
If you paint the lockers, it becomes the set for Victorious.
Running the Asylum: "iOMG" and "iLose My Mind" Sam/Freddie romance arc episodes utterly match several of the biggest Fandom-Specific Plot lines and the most common fanfic tropes. Sam and Freddie end up Locked in a Room together at the school. Sam giving Freddie a Forceful Kiss to clear up that Sam actually likes him. Carly becoming a Shipper on Deck and Freddie returning Sam's feelings without any explanation or closure for his feelings for Carly.
Schedule Slip: As described in Screwed By The Network right below.
Screwed by the Network: After season three, Nick has taken a decidedly inconsistent approach to the show. It only orders 13 episodes at at time compared to the 26 or so that it was doing in the first three, it airs the show at random times, advertises that the entire season will be played every week, then stops it after 3 episodes, puts on new episodes with little advertising, and then starts putting them on at weird times, such as Wednesday the 28th of December for the second blooper episode, and then 8-9pm New Year's Eve for the "iPsycho" sequel. Admittedly, Dan Schneider has to take some of the blame, as he seems to have poor time management, which means Nick were only ordering 13 episodes of both iCarly and Victorious when they could have fit full seasons in even with the studio split (the two shows share the same studio space, and can't film when the other is filming) taken into account. This odd handling of the show and its timeslots is one the bigger reasons for the abysmal ratings for Season 5 compared to seasons 2, 3 and 4.
Scully Box: Freddie/Nathan had to use the shoe version in Season 1 due to not having gone through puberty yet. He has massive platform shoes. By Season 2 this was unnecessary and he was about the same height as Carly/Miranda, by Season 3 he's grown even more, so much that during "iSpeed Date" Carly/Miranda can place her head in the crook of his neck and it fits perfectly.
Jennette/Sam starts wearing platform shoes during Season 4 for the same reason that Freddie/Nathan did in Season 1.
Shoe Slap: Purposely averted. If you watch "iGo to Japan", you'll notice Miranda and Jeanette are barefoot for the entirety of the first scene. They were in swing sets temporary mounted on the ceiling and constantly swinging toward the camera. To avoid any mishaps with the camera and loose sneakers launching into them, they slipped off their shoes, sat them down mostly out of view on set, and shot the scene with bare feet. Jeanette can be seen scooping up her sneakers as she pads down the hallway after high-fiving Miranda.
Shrug of God: Ask Dan Schneider a question about Seddie or Creddie. It will be a miracle if you get a straight answer back. The more 'intelligent' the question, the less likely he will even respond at all. The dumbest, or least focused questions might get the question thrown back at them in a different way.
Suppressed Mammaries: In between Season 1 and 2, Nathan Kress (Freddie) grew up... and Jennette McCurdy (Sam) grew outward. Since then, the show began tot take o wrapping Sam up in layers of 3 or 4 t-shirts, but she kept on growing. In a few episodes in season 3 they forgot about this, such as the rabbi scene in iSaved Your Life, and it's pretty obvious what they were doing. By season 4, Jennette continued growing, to the point that the multiple layers of t-shirts don't really hide her chest anymore, and they could just about get away with looser clothing, but even then... All pretense of covering her up was gone now, about 1/3 of the way through Season 4.
"Take That!" Tit-for-Tat: Disney Channel and Nickelodeon had a minor feud going during The Noughties, mainly playing out through stories and devices in iCarly and Sonny with a Chance. iCarly has an episode where it takes shots at the Disney Channel (a.k.a. "Dingo" Channel), for In-Universe stealing the ideas of iCarly.com. They also claim that the original ideas of the channel are bland and unentertaining, and they make all their adult characters stupid. Sonny With a Chance got to have its own go with So Random! going to hell with new producers in a storyline that is mocking Nick's All That. iCarly then counters again with an entire episode dedicated to completely unsubtly criticise a certain network's new interpretation of kids' TV and their programming overhaul that ditched all of the 'good' children's TV shows in favor of lesser and more demeaning ones.
Listen to how Gibby delivers his line: 'Uh-oh! Looks like trouble off the stern... port... bow.' You'll notice how he seems confused and slows down at the end of that line. The reason? Noah ("Gibby") forgot the line as he was saying it! He couldn't remember how it ended. Later, when I watched it in editing, I felt it played really funny, so I used the take where he forgot the line.
Why Fandom Can't Have Nice Things: Before Season 3 had started airing, Dan posted a script fragment from a future episode◊. He took it down quickly, but it was reposted on various sites. Naturally, shippers from both sides went nuts, especially on LiveJournal. After heavy criticism about Dan ruining the fandom and the LJ communities with his interaction he quit and deleted his LiveJournal, without warning or notice (meaning the fandom lost a lot of interesting interaction with him), and eventually setup his own blog site, which he claimed was for better control, but his first post was about being pissed off with reponses to his script.
Word of God: Dan Schneider. Very carefully avoids Lying Creator by using ambiguous meanings, hypothetical, counter-questions in response to questions and shrouding common shipping viewpoints in terms of what "his friends" might think about what's happening. Was very active in the fandom up to the start of Season 3, although not as much now that he's dealing with Victorious as well as the 4th season of iCarly.
Taken to the extreme with his post about the finale "iGoodbye". After seeing backlash about his failure to make the Seddie pairing canon while he made Creddie canon via a typical Last Minute Hookup, he wrote a blog that could be described in short as "completely inverting the meaning of what just took place on screen" by attempting to claim the Last Minute Hookup, the romantic moment Carly comes up to the studio, takes Freddie by the hand then kisses him just moments before leaving for Italy may have actually been a platonic 'friendship' kiss. This did not go down well in the fandom, with people calling him out for the Blatant Lies, many female viewers were especially upset about the idea that they just go around passionately kissing their male friends to show their friendship. This is a good example of Word of God actually making the understanding of what took place on their show less clear. Then again, it was likely deliberate as Dan has the new Spin-OffSam & Cat, and he wanted to dangle the potential of the Seddie relationship picking up on that show to get more viewers. Most people in the fandom have simply ignored him and have gone by what took place on screen.
What Could Have Been: The original name of the Carly character was going to be Sam. The female sidekick was going to be called Kira. But they couldn't get the iSam domain name. So Sam became Carly, and Kira became Sam. This has the curious effect of swapping around the Portmanteau Couple Name of both major ships. The Just Friends Creddie ship would have been known as Seddie, while the Jerkass Seddie ship would have been known as Kreddie. It would have a minor impact on the Les Yay Cam ship by changing the name from Cam (Carly/Sam) to Kam (Kira/Sam).
Dan Schneider originally explored a straight Drake & Josh spin-off as a Miranda Cosgrove vehicle, with Miranda naturally reprising her role as Megan Parker, but ultimately he felt dissatisfied with every idea centered around that concept he could think of. He then explored the idea of a fresh concept and character that was getting closer to iCarly, but centered around a girl who suddenly found herself getting her own variety TV show. He got as far as writing the script for the pilot - and then threw it in the trash, once again being dissatisfied. He then changed the "TV show" to "web show", and things finally started to click.
A second iCarly spin-off centered around Gibby (and titled as such) had a pilot filmed but was not picked up. As originally envisioned by Dan, it would have ran alongside Sam & Cat and Victorious.
In-universe example: If Spencer was born normal, Carly and Nevel would be girlfriend and boyfriend, much to Carly's horror.
Sam's sock full of butter that she uses as a weapon in "iTake on Dingo" was originally going to be a sock full of quarters, but the powers that be decided that'd be too violent, since if a viewer decided to try it, it could actually do some damage. Probably for the best, as a sock full of butter is funnier anyway.
Word of God: Dan Schneider reveals in a blog post that they shot two different versions of the ending to iOMG; one where Carly never witnesses Sam and Freddie kiss near the end, and one where she does witness it. The second version is what made the final cut.