Polyforms, literally “many forms,” are shapes that are built up from basic unit forms such as squares, triangles, hexagons, or circles. Polyforms built of squares use the “-omino” ending. There is only 1 domino, built of two squares, but there are 2 trominoes built of three squares, 5 tetrominoes built of four squares, 12 pentominoes built of five squares, 35 hexominoes built of six squares each, etc.