Game juice
The extra layer of feedback — shakes, particles, bounce and sound — that makes an action feel satisfying without changing the rules of the game.
"Juice" is all the non-essential feedback a game gives in response to the player's actions: screen shake, flashes, particles, squash-and-stretch, easing on movement, hit pauses and sound, layered up to confirm every button press. The rules are identical with or without it — but without it the game feels dead.
The idea was popularised by Martin Jonasson and Petri Purho's talk "Juice it or lose it" (2012) and by Vlambeer's Jan Willem Nijman, whose "The art of screenshake" (2013) showed how much of the Nuclear Throne feel lived in tiny effects. Juice is cheap polish with a big payoff, though in excess the screen becomes a chaos of shakes and particles.