Variable jump height
The jump rises higher the longer the jump button is held — a tap gives a small hop, a long press a full jump.
A fixed-height jump forces the player to reach every ledge in exactly one way. Variable jump height hands back control instead: release the button early and the upward velocity is cut immediately, and the character begins to fall. The upshot is that a single button covers both a small step onto a crate and a full leap across a chasm.
The technique is usually credited to Super Mario Bros. (1985) and has been genre standard ever since. It is implemented either by zeroing upward velocity on release, or by applying heavier gravity during the rising phase — usually in the same character controller that handles air control.