The Tetromino is any shape constructed using four squares arranged orthogonally. There are only five possible permutations, called the "Free tetrominoes."
The Tetrominoes feature prominently in many video games, starting in Tetris, where they are actually called Tetriminoes. Tetris' success caused a massive pop culture boom around the game and inspired hundreds of games to come, some of which also featured Tetrominoes. Even today, some games (such as Fez and Rymdkapsel) are made with those shapes playing a key role, often as a direct homage to Tetris.
List of Tetrominoes:
Other names include straight, stick, and long. This is the only tetromino that can clear four lines outside of cascade games.
Other names include square and block.
Other names include inverse skew and right snake.
Other names include skew and left snake.
Other names include gamma, inverse L, or left gun.
Other names include right gun.