i'm quite passionate about polyominoes of all shapes and sizes, due to working with blokus and pentomino codes.

a polyomino is a geometric figure formed by joining squares of equal size, edge to edge.

there are only a few practical polyomino forms:

- TROMINO: three squares - there are only two forms of this, I and L.
- TETROMINO: four squares - there can be either five or seven forms of this. I, T, O, L, S, and potentially J and Z, though they may be grouped under L and S respectively
- PENTOMINO: five squares - there can be 12 or 18 forms of this. the 12 'free' pentominos, by the general definition, form F, I, L, N, P, T, U, V, W, X, Y, and Z. if you rotate the pentominoes, you can also make R, S, Q, C, another variant of N, M, and S.

these are the only variants you will see in a practical environment. 'hexominoes' are the variant for six pieces, and is the last available variant you can tile each individual form of into a square. there are 35 versions of this, so, not exactly practical for use. they aren't coded to letters, either, so why even bother.

there's also a 'monomino' and 'domino', which each only have one variant - a single square or two squares adjacent - though a domino can be oriented in 2 different ways

a tetris game, as it is named for, is played with a set of 7 tetrominoes.

blokus, one of my favorite things (i say 'thing' and not 'game' because i don't play it i use the pieces for stop motion animation) uses a set of 21 different pieces, including every free tromino, tetromino, pentomino, and additionally bears a monomino and domino. this makes for a total of 84 pieces in a set, because there are four colors.