Piece
A piece in Tetris and similar games is a geometric shape consisting of a set of blocks that is moved as a unit. A block is part of a piece. In some games, all blocks that make up a piece are colored the same; in others, especially falling piece games other than Tetris and its clones, they are colored differently.
Polyominoes
A polyomino is a piece made of two or more square blocks, where all blocks are connected through full coincident edges (as if squares on graph paper).
- A free polyomino is one that may be translated (moved about), rotated, or reflected.
- A one-sided polyomino is one that may be translated or rotated.
- A fixed polyomino can only be translated.
Polyominoes come in several sizes:
- 2 blocks: Domino (featured in Dr. Mario and Puyo Pop; seen in Tetris Blast)
- 3 blocks: Tromino (or trimino): featured in Columns (fixed I only) and Pac-Attack (L only; seen in Tetris Blast)
- 4 blocks: Tetromino (or tetramino or tetrimino) (featured in Tetris and its clones; Lumines uses only O tetrominoes)
- 5 blocks: Pentomino (featured in Daedalian Opus; seen in Tetris 2 + Bombliss).
Polyominoes are often named by their shape. For instance, an "I" has all its blocks in a straight line, and a "T" consists of an "I" with one or more blocks in a straight line connected to the center of the "I".
Hinged polyominoes
A hinged polyomino is similar to a polyomino but also allows connections at a point. In games that use hinged polyominoes, the pieces may break apart when they land, and they may or may not be controllable after they break.
- 4 blocks: Hinged tetromino (featured in Tetris 2).