A small rectangular block of wood or plastic with a line down the middle and an arrangement of dots resembling those on dice. A domino can be played by a player or set out in rows in such a way that when one is tipped it will cause the adjacent pieces to fall over, starting a chain of events that can lead to great complexity. This principle is the basis of many games played with dominoes, and led to the use of the term a domino effect (an event that starts out minor but ends up having significant consequences) in the popular imagination.
Dominoes are normally twice as long as they are wide and are thick enough to be stood on end. Each side of a domino has an identity-bearing surface called an end that is marked with an arrangement of spots, or pips, that determines the value of the tile; each end may be either blank or identically patterned to the other.
Most modern sets of dominoes, including those used in professional play, contain 28 tiles. This allows for a wide variety of games that are generally divided into two categories: blocking and scoring games. The blocking games require a domino to be placed in a position such that the open ends of that domino are lined up with the open ends of the domino that is already in place. This is done by a process called “matching”.
After a domino has been matched to its neighbor, the remaining open ends can be filled in at random by the players. As the domino chain develops, a snake-line pattern is often seen, and if a double is present, it must be played square to its neighbor to produce an uninterrupted chain.
During a game, players score points by counting the total number of pips on opposing player’s dominoes. A domino that can’t be played is called a dead Domino, and the winner is the player who makes it playable by either blocking it with another of his or her dominoes or scoring a large number of points in a specified number of rounds. Usually, a domino that scores a point is awarded the count of all the pips on its neighboring dominoes, but some games count only the sum of the numbers on adjacent pairs of dominoes (e.g., a 6-6 countes as 12).
In the past, dominoes were often used to teach children about probability. They were a good example of how a simple action can result in an outcome much greater than its initial starting point, because each domino could be knocked over by a single other domino that was only slightly larger than the first one. In more recent times, however, dominoes have become increasingly popular with adults as a form of relaxation and entertainment. Many people play them at home with friends and family, although it is also possible to compete against others in domino tournaments.