Jump buffering
Remembering a jump press for a few frames so a jump the player pressed just before landing still fires on touchdown.
Human timing is imprecise, and a platformer that only jumps on the exact frame the button is down and the character is grounded feels broken — the player presses a hair early and nothing happens. Buffering stores the input for, say, five to ten frames and spends it the moment the character becomes grounded, turning a near-miss into a clean jump.
It is the landing-side twin of coyote time, which forgives a press just after leaving a ledge. Neither changes what is physically possible; both widen the window the player must hit, and together they are most of why a game "feels tight." Celeste (2018) turned both techniques into common knowledge among indie developers.