What is "tetromino"

n. (context geometry English) A polyomino made up of four squares.

A tetromino is a geometric shape composed of four squares, connected orthogonally. This, like dominoes and pentominoes, is a particular type of polyomino. The corresponding polycube, called a tetracube, is a geometric shape composed of four cubes connected orthogonally.

A popular use of tetrominoes is in the video game Tetris, where they have been called Tetriminos (spelled with an "i" as opposed to the "o" in "tetromino") since 2001.