A domino is a small rectangular wood or plastic block, thumb-sized and bearing from one to six dots or pips, resembling those on dice. A complete set consists of 28 such dominoes. The term is also applied to a game played with such pieces, wherein they are placed on a surface in lines or angular patterns and then allowed to fall. A domino effect occurs when a single event affects a larger number of people or things than expected. The concept is similar to that of a nerve impulse, which is transmitted from a neuron at one end of its axon to other neurons in the same brain cell, and to other cells in the body.
A game played with dominoes may involve scoring points, or simply providing entertainment for a group of people. Some games are based on strategy, others require a great deal of luck. Most of the rules for playing dominoes are determined by the specific game being played. However, there are some general rules that apply to all domino games.
The most common rule is that the first player must place a domino to start the chain. Typically, the first domino placed must be a double, and must have matching ends. The other ends of the domino placed must be touching each other or a tile already played, and can be either square or cross-ways across the center of the chain. This allows the chain to develop into a snake-line, according to the rules of the particular game being played.
Players then draw tiles for their hand, according to the rules of the game being played. The number of tiles drawn depends on the rules and the size of the hand. If a player draws more than he is permitted to, the extra tiles are called overdraws. The player must pass or bye those tiles to the person to his right, who then takes them and adds them to his own hand. In some games, the excess dominoes remain in the stock and can be bought later in the game (See Passing and Byeing).
Once a player has drawn his hand, he places a tile on the bottom of the line of play, or board. The next player then makes his play. The order of play is determined by the rules of the specific game being played, but generally each player must follow the basic instructions listed here under Line of Play before making a play.
Many domino games involve forming a line of dominoes by matching the pips on the open ends of the pieces, or by placing them side-by-side to form a shape. Some of these forms include straight lines, curved lines, grids that make pictures when they fall, and 3D structures such as towers and pyramids. Depending on the game being played, some of these can be very complex and take a long time to set up. Other games are very quick and easy to play.