The highest-scoring four-line clear in most Tetris versions is called a Tetris.
A Tetris happens when a player completes four horizontal lines at once, normally by dropping the long I-shaped tetromino into a one-column gap. Because each standard tetromino contains four blocks, an I piece can span the full width of a conventional ten-column playfield and remove four rows simultaneously.
The term is a play on the game's name and the Greek-derived prefix tetra, meaning four. Clearing four lines is usually rewarded more generously than clearing one, two, or three lines, although exact scoring depends on the game's rules, level, and scoring system.
A Tetris is not the same as a T-spin, perfect clear, or combo. A T-spin involves rotating a T-shaped piece into a tight space; a perfect clear empties the playfield after a clear; and a combo rewards consecutive line clears. Some modern games add special bonuses, so “highest-scoring” is a general convention rather than an absolute rule for every variant.