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A geometric puzzle centered around geometric figures formed from unit-squares.

A polyomino is a plane geometric figure formed by joining one or more unit-squares edge to edge. Equivalently, a polyomino is a finite subset of the regular square tiling with a connected interior.

Typical examples of polyominoes are:

  • the 2x1 dominoes (consisting of 2 squares)
  • the straight 3x1 tromino and the L-shaped tromino (both consisting of 3 unit-squares)
  • tetromino pieces (consisting of 4 squares), as used in TETRIS
  • pentomino pieces (consisting of 5 squares); there are 12 pentominoes, up to rotation
  • hexomino pieces (consisting of 6 squares)

By definition, polyominoes (consisting of 8 or more squares) may contain holes. For some puzzles (such as tiling problems), polyominoes with holes are inconvenient. Polyominoes without holes are called simply connected polyominoes.

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