Tetromino

A tetromino, sometimes called tetramino or tetrimino, is a four-squared polyomino. The seven tetrominoes are I, O, T, S, Z, J, and L.

I
Other names include straight, stick, and long. This is the only tetromino that can clear four lines outside of cascade games.

O
Other names include square and block.

S
Other names include inverse skew and right snake.

Z
Other names include skew and left snake.

J
Other names include gamma, inverse L, or left gun.

L
Other names include right gun.

Multimino
In The Next Tetris, Sticky mode of Tetris Worlds and Tetris Mania, and Jewelry Master, some tetrominoes are multiminoes, that is, the tetromino itself is divided into visible components. Though the tetromino is moved and rotated as a unit, once it locks, the individual components fall.