A domino is a flat, thumb-sized rectangular block of wood or plastic that has one face bearing an arrangement of dots (often referred to as pips) similar to those on dice. 28 such dominoes make up a complete set. Also called bones, cards, men, tiles or tickets, they can be used for playing a variety of games.
Dominoes are most commonly used for positional games in which each player in turn places a domino edge to edge against another, so that the adjacent ends of the two pieces match either in number or in some other specified property. The resulting chain of matching pairs is then used to form the basis for further play. In some games, the chains are used to score points or otherwise influence the outcome of the game.
The individual pieces are normally twice as long as they are wide, so that they can be easily stacked and arranged. They are usually colored white on the top and black on the bottom, but there are many other variations. Dominoes are usually made from a material such as bone, silver lip ocean pearl oyster shell (mother of pearl) or ivory with a contrasting color on the pips. More recently, sets have been made from other natural materials such as marble and soapstone; metals including brass and pewter; or even ceramic clay. Such sets tend to be much more expensive than those produced from polymer materials.
In positional games, the dominoes are arranged on a flat playing surface in a line or a series of angular patterns. Depending on the rules of the particular game, the lines of play may be either crosswise or lengthwise. In some games the players agree to limit the number of times a double can be played. If a player does not follow this restriction, the other players may “stitch up” the end of the line of play so that the double is no longer a valid move.
When the initial domino is placed, it is called the set, the down or the lead. The word is also used to describe the first tile played in a round of a game, or an entire round itself.
Once a domino is played, it must be followed by another tile of the same type. This continues until the game is completed, at which point a winner is declared and the winning hand is rewarded or punished according to the rules of the particular game. In some games, the players draw new hands if no player holds a valid double tile, or the players take turns shuffling before each game. In other games, the player who wins the previous game takes the first turn in the next game. The word domino also refers to the fact that certain types of tiles are more valuable than others. For example, the largest double tile is known as a heavy tile. The term is also sometimes used to refer to the process by which a domino effect develops, when small changes in behavior trigger an avalanche of additional changes.