thumb|right|A nonomino or [[Jigsaw puzzle|Jigsaw Sudoku puzzle, as seen in The Sunday Telegraph]]
A nonomino (or enneomino or 9-omino) is a polyomino of order 9; that is, a polygon in the plane made of 9 equal-sized squares connected edge to edge. The name of this type of figure is formed with the prefix non(a)-. When rotations and reflections are not considered to be distinct shapes, there are 1,285 different free nonominoes. When reflections are considered distinct, there are 2,500 one-sided nonominoes. When rotations are also considered distinct, there are 9,910 fixed nonominoes.
Symmetry
The 1,285 free nonominoes can be classified according to their symmetry groups: Therefore a complete set cannot be packed into a rectangle and not all nonominoes have tilings. Of the 1285 free nonominoes, 960 satisfy the Conway criterion and 88 more can form a patch satisfying the criterion. Two additional nonominoes admit tilings, but satisfy neither of the previous criteria. This is the lowest order of polyomino for which such exceptions exist.
One nonomino has a two-square hole (second rightmost in the top row) and is the smallest polyomino with such a hole.
File:The 37 Nonominoes with Holes.svg