Production Nickname

When something in a show receives a Fan Nickname which originated with the show's production team. Doesn't count if it's a technical term which can be applied to unrelated shows.

If the series runs long enough, the term runs a high probability of becoming either canon or an in-universe nickname.

Comics

 * The DC Comics writing staff has a long tradition of referring to Mr. Mxyzptlk as "Bill" to sidestep the issue of how to pronounce his name.
 * Mix-zees-pit-lick, according to one book.
 * In the animated series, he does a rebus showing it as mix-Yess-spit-lick (blender, band 'Yes' styled logo, tongue doing wet raspberry, tongue licking).

Film - Animation

 * The animators for The Hunchback of Notre Dame decided to nickname Frollo's horse Snowball. This has caught on with fans, thanks to an audio commentary, and retroactively also became the name of Jafar's horse and the monster pulling Hades' chariot.
 * The sequence for the song "Hellfire" was nicknamed "Mr. Frollo's Wild Ride" by the animation team.
 * The roach in WALL-E is named Hal.
 * Hal Roach, geddit?

Film - Live-Action

 * The shark in the movie Jaws was nicknamed Bruce, after Steven Spielberg's lawyer.
 * "Clover" from Cloverfield.
 * "Steve Buscemi", the monster from The Host.
 * Doc Ock's tentacles in Spider-Man 2 were dubbed Moe, Curly, Larry and Joe.
 * The clown puppet in Saw is named Billy.
 * While filming Manos: The Hands of Fate, Harold Warren's crew called the film Mangos: The Cans of Fruit behind his back.
 * The creature from "The Crate" segment of Creepshow was nicknamed "Fluffy" (it even illustrates Fluffy the Terrible).
 * In Alien vs. Predator: Requiem, the Predator was nicknamed Wolf (after Winston Wolf) and the Predalien was nicknamed Chet (after Bill Paxton's character in Weird Science).

Literature

 * While writing the Harry Potter series, J. K. Rowling mentally used the term "The Big Seven" to refer to Harry, Ron, Hermione, Neville, Ginny, Luna, and Draco.

Live-Action Television
"Mitchell: I'm sorry, the what?
 * The Pepperpots (Pythons in old lady drag) in Monty Python's Flying Circus.
 * Star Trek, starting with The Next Generation, has "Okudagrams" - the displays on the touchscreens and monitors - after their creator Michael Okuda.
 * The engineering access tubes were dubbed "Jeffries tubes", which was a Canon name by TNG.
 * Irving A. Feinberg was the property master for Star Trek: The Original Series. The little gizmos he came up with for the show (such as the medical scanner and the laser scalpel) were nicknamed "Feinbergers" by the cast and crew. The usage later spread to the fanbase.
 * Similarly, the wall panels were often labeled with seemingly nonsensical phrases, like "GNDN435". This actually stood for "Goes Nowhere, Does Nothing", indicating the just-for-looks nature of all the pipes and wires in the Enterprise's interior.
 * Caprica-6 from Battlestar Galactica, although that eventually made it into the show dialog as well.
 * HRG (Horn-Rimmed Glasses) in Heroes.
 * The concentration face Hiro Nakamura makes in order to travel through time or space is apparently called the "squishy blinky" by the production crew.
 * The pterodactyl, Myfanwy, in Torchwood.
 * The Barracks on Lost are called "New Otherton" by production, which spread to fans and then incorporated into dialogue as Sawyer's nickname for the place.
 * On Stargate SG-1, "kawoosh" was a production nickname used to describe the "unstable vortex" formed when a Stargate opens. The term wasn't used on the show until the episode "Crusade", in which it was coined in-universe by Samantha Carter:

Carter: The unstable vortex of a forming wormhole. Kawoosh!

Mitchell: Don't think I've ever heard you call it that before.

Carter: Really?

Mitchell: Don't get me wrong, it's good."

Video Games

 * In Portal, the portal maneuver was called "flinging," and the Aperture Science Material Emancipation Grid was dubbed the "fizzler". The absent character who left behind dens and scrawlings on the walls was named the Rat Man (for his scrounger-in-the-wall habits). Later, he was promoted to a first-order character via an interquel comic book. His real name is Doug Rattman.
 * The main character of the Wing Commander series originally had no default name, but the production crew called him Bluehair. He was later given the name Blair as a nod to this.
 * During development, VVVVVV was simply called "V" by its creator Terry Cavanagh.
 * Guybrush Threepwood, hero of the Monkey Island franchise, was named Guybrush from the file containing the "guy-brush" the developers used to animate his sprite. It stuck as his name.

Western Animation

 * The One-Winged Angel form of the Ocean Spirit in Avatar: The Last Airbender was called Koizilla during production. You'd be hard-pressed to find anyone that calls it anything else. Heck, it's a 90-foot carp. Half the people using the term probably coined it independently.