The Tetris term for clearing four horizontal lines at once is a Tetris. It is the highest standard line-clear in classic Tetris and normally requires the long, four-block-wide I tetromino.
Players create the setup by leaving a one-column gap in a tall stack, then wait for the I piece to fall vertically into that space. Completing four rows simultaneously removes them at once and awards a larger score than singles, doubles, or triples in many versions. The exact scoring formula varies by game and level.
The word is both the game’s name and its traditional name for this maneuver. It is not the same as a perfect clear, which removes every block from the playfield, or a T-Spin, which describes rotating a T tetromino into a tight placement. A combo refers to clearing lines in consecutive drops, so none of those terms specifically means four lines at once.