Wiktionary
hard drop
n. A manual downward motion of a piece that makes it land immediately (that is, within only one frame) and is possible in multiple versions of the video game ''Tetris''.
Usage examples of "hard drop".
He landed on cement at the bottom, but it was not a hard drop at all, only a flex of the knees.
He stuck his head out and looked straight down to the stone plaza, a hard drop of some two storeys below.