Pentomino

A pentomino is a shape made of five equal squares joined edge to edge, a polyomino of order five whose name comes from the Greek word for five combined with domino. Counting shapes that differ only by rotation or reflection as the same, there are 12 free pentominoes; treating mirror images as distinct gives 18 one-sided pentominoes, and treating rotations as distinct as well gives 63 fixed pentominoes. Pentomino tiling puzzles and games are popular in recreational mathematics, and video games that imitate Tetris, as well as Rampart, usually use the full set of 18 one-sided pieces, whereas Tetris itself uses four-square pieces called tetrominos. Each of the twelve free pentominoes satisfies the Conway criterion, so every one of them can tile the plane, and each chiral pentomino can do so without being reflected.