Polyiamond

A polyiamond (also polyamond or simply iamond, or sometimes triangular polyomino[1]) is a polyform whose base form is an equilateral triangle.

The name was suggested by recreational mathematics writer Thomas H. O'Beirne in New Scientist 1961 number 1, page 164.

Some authors also call the diamond (rhombus with a 60° angle) a calisson after the French sweet of similar shape.

Like polyominoes, but unlike polyhexes, polyiamonds have three-dimensional counterparts, formed by aggregating tetrahedra.

The set of 22 polyiamonds, from order 1 up to order 6, constitutes the shape of the playing pieces in the board game Blokus Trigon, where players attempt to tile a plane with as many polyiamonds as possible, subject to the game rules.