Dominoes (or "ominos") generally refers to the individual or collective gaming pieces making up a domino set (sometimes called a deck or pack) or to the games played with dominoes these pieces. In the area of mathematical tilings and polyominoes the word domino often refers to any rectangle formed from joining two squares edge to edge. Standard domino sets consist of 28 pieces called bones, cards, tiles, tickets, stones, spinners or dominoes. Each bone is a rectangular tile with a line dividing its face into two square ends. Each end is marked with a number of black spots (also called pips) or is blank. The spots are generally arranged as they are on six-sided dice, but because there are also blank ends having no spots there are normally seven possible faces. Standard domino sets have ends ranging from zero spots to six spots (double six set), but specialized sets might range from zero to nine (double nine set), zero to twelve (double twelve set), zero to fifteen (double fifteen set), or zero to eighteen (double eighteen set). The back side of a domino is generally plain, or is decorated in the same manner on every piece. Dominoes have been made of bone, ivory, plastic, metal and wood, and occasionally are made of card stock like that for playing cards. Dominoes are rather generic gaming devices. Many different games can be played with a set of dominoes.