Idle animations refer to animations within video games that occur when the player character does not do any action (hence being idle). These sorts of animations are largely popular with action games, where players may rarely be idle and thus serve as easter eggs. One of the first games ever to introduce idle animations on a mainstream basis was Maziacs; the sprite taps his feet, blinks, and sits down. This trend spread to many other action genre games, becoming more complex as allowed by the advancing hardware. For example, in Donkey Kong Country 2: Diddy's Kong Quest, Diddy Kong juggles a few balls if the player offers no controller input for a few seconds.
Idle animations in modern 3D games are used to keep them realistic. In general, games meant for younger audiences are far more likely to have complex or humorous idle animations, while games for older people tend to have more basic idle animations. For example in Super Mario 64, Mario will occasionally look around, and eventually fall asleep, while in others, steady breathing suffices as an idle animation.
Commander Keen 4: Keen becomes impatient, tapping his foot then sitting down to read a book. There is also an easter egg: the first time Keen becomes idle when standing on one of the moon symbols in the Pyramid of the Moons, instead of the above sequence he "moons" the player.
Duke Nukem 3D: Duke will crack his knuckles and comment to the player impatiently, "What are you waiting for?"
Future Knight (ZX Spectrum version): the hero starts to get annoyed and, after a while, will start losing energy until game over occurs.
Grand Theft Auto IV: Niko Bellic will yawn, inspect his gun, stretch, scratch his head etc. If outside in the rain he will catch the rain and shake off his soaked clothes.
Half-Life if one is holding a Snark, it will attempt to bite the hand holding it. Gordon will then admonish it with his left index finger, almost getting bitten in the process. All other weapons have an idle animation as well.
Halo series, Master Chief will inspect his gun, along with other things after standing a while.
Just Cause: Rico will flip his dual wield pistols.
Kirby: Squeak Squad: Kirby will fall asleep and dream of Strawberry Cake until he wakes up, when he swallows the dream cloud.
Metal Slug: Marco Rossi will drink from his bottle (Tarma Roving does the same), Eri Kasamoto will eat her bubblegum and blow a balloon with it, and Fio Germi will sit and eat a sandwich akin to a picnic. When wielding their powered-up weapons, Marco and Tarma will briefly play with what appear to be a snake while Fio and Eri will get exhausted and flick their wrists out of fatigue.
Pokémon Black and White introduces idle animations for all Pokémon during battle. If the device is left alone for a while during a battle, the camera will zoom in on a Pokémon as it does its animation.
Rayman 2: Rayman will take his body, and bounce it like a basketball. He will spin it on his finger, then put it back.
Resident Evil: Chris crosses his arms and waits. Jill puts her left hand on her hip and pats her gun against her leg with her right hand.
Ristar: the character will perform a unique idle animation depending on what stage he is on. For example, on the snow-themed stage, he will make a little snowman and on the music-themed stage he will start to dance happily.
StarCraft: the images for the units will look around after a given time.
The King of Fighters: Ralf Jones will hop once before returning to his usual stance, Ryuji Yamazaki will flick his left arm before beckoning his opponent and returning to his usual stance (the beckoning was removed in The King of Fighters 2003 and the flick wasn't introduced until The King of Fighters '97), Billy Kane will twirl his staff before returning to his usual stance, and K' will stand straight with one hand in his pocket, blinking at a slower rate within each time until he falls asleep without returning to his usual stance unless he moves, attacks, or is attacked.