Definition:Dominoes

Definition
Dominoes are a set of (usually) wooden tiles:
 * in the shape of an oblong $2$ units by $1$ unit (of the order of an inch)
 * with two numbers, usually in the form of dots, usually between $0$ and $6$, one at each end, divided by a line between them, on one side only
 * such that each of the numbers appears paired with every number (including itself) exactly once
 * such that the opposite sides of the dominoes are unmarked so as to make them indistinguishable when upside down (although of course they may have a pretty design on them).

Their usual purpose is as the basis of various games, but feature significantly in the realm of recreational mathematics.
 * Dominoes.png