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A tetromino, also called a tetramino or tetrimino, is a geometric shape composed of four squares, connected orthogonally.^{[1]}^{[2]} 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.
Contents
The seven tetrominoes
Ordinarily, polyominoes are discussed in their free forms, which treat rotations and reflections in two dimensions as congruent. In that case, there are five unique tetrominoes. However, due to the overwhelming association of tetrominoes with Tetris, which uses onesided tetrominoes (making reflections distinct but all rotations congruent), people recognize seven distinct tetrominoes:
 I (also called "stick", "straight", "long", "line"): four blocks in a straight line
 J (also called "inverted L" or "Gamma"): a row of three blocks with one added below the right side.
 L (also called "gun"^{[3]}): a row of three blocks with one added below the left side. This piece is a reflection of J but cannot be rotated into J in two dimensions; this is an example of chirality. However, in three dimensions, this piece is identical to J.
 O (also called "square",^{[3]} "package", "block"): four blocks in a 2×2 square.
 S (also called "inverted N", "reverse squiggly", "szigzag"): two stacked horizontal dominoes with the top one offset to the right
 Z (also called "N", "skew", "snake",^{[3]} "squiggly", "zzigzag"): two stacked horizontal dominoes with the top one offset to the left. The same symmetry properties as with L and J apply with S and Z.
 T: a row of three blocks with one added below the center.
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