Dominoes are a type of game piece that can be used to play many games. They are normally twice as long as they are wide and are rectangular in shape, with one side displaying a pattern of dots or pips and the other blank or identically patterned. Each domino has a designated value, indicated by the arrangement of its pips, that is compared to a specified total, usually a number, and when two or more tiles have the same value they are referred to as matching. Those with a number on both ends are referred to as doubles, while those with no numbers on either end are called singles.
The most common domino sets are composed of double-nine, or 55 pieces, but larger sets can also be found. These are referred to as extended sets, and are usually composed of several additional types of dominoes that add extra functionality to the set. For example, more dominoes with fewer pips are added to the set, giving more options for matching up tiles. A typical extended set includes double-nine, double-12, double-16, and double-18 dominoes. In addition to this, some extended sets feature more specialized dominoes that allow the player to play more complicated games such as a variant of Concentration, or even build 3D structures such as towers and pyramids.
Once the dominoes have been drawn, the first player (determined either by drawing lots or by who holds the heaviest hand) begins placing them on the table in order to begin building chains of matching tiles. The chain can be laid out on a flat surface such as a table or a floor, or it can be built into walls, or even stacked to create 3D structures. The first domino is placed with its long edge touching the edge of the tile already on the table, and a subsequent tile must be played to straddle that end of the chain. Since each domino has a specific value, the player must be careful not to place a tile that will cause an unwanted result.
Some dominoes have special sides that can be used as a target for other players to hit with their dominoes, while others are known as wild and may be matched up to any other tile in the chain. The rules of each game dictate how these wild or special sides can be used, and some games allow the players to make their own rules in a creative way that adds to the fun.