A polyomino of the fifth order; five connected squares.

The twelve pentominoes are:

X  XX  X   X   XX  XX  XXX  XXX  XX   XX    X   XX
X  X   XX  X   XX  X   X     X    XX   XX  XXX   X
X  X   X   XX  X   XX  X     X     X   X    X    XX
X  X   X    X
These twelve shapes are the subject of many tiling puzzles and other recreational mathematics. The most well-known tiling problem involving these shapes is the tiling of a rectangle using each pentomino once. Because their total area is 60, several rectangles are possible: 3x20, 4x15, 5x12, 6x10.