Domino is a small rectangular block used for playing games of chance or skill. Each domino has an identifying mark on one side, while the other is blank or has a pattern of spots, like those on dice, which may differ from each other (a 6-6, for example, counts as two). A set of dominoes usually contains 28 tiles. Dominos can also be made from other materials, including stone (e.g., marble or granite); other hardwoods such as ash, oak, redwood, and cedar; metals such as brass or pewter; ceramic clay; and even glass or crystal. Historically, sets were crafted of bone or ivory; later, ebony and other dark woods were used. In modern times, plastic is often used.
Dominoes are most commonly used for positional games in which each player takes turns placing a domino edge-to-edge against another so that the adjacent faces of the two tiles match or form a specified total. The number of pips on a domino determines its value in the game. A domino with a single-pips face is known as a double, while a domino with a different number on each half of the face is called a combination. A combination of dominoes with different numbers on each face is called a doublet.
Most dominoes are numbered using either traditional Latin numerals or a system of dots, called pips, that resemble those on a die. The pips are arranged in groups of two or three, and each domino has an odd number of pips on the left half and an even number on the right. If a domino has both an odd and an even number of pips, it is referred to as a mixed-pair.
When a domino is played so that it touches a previous domino with an open end, the opening ends of both dominos are said to be “stitched up.” If a tile is placed cross-ways on a domino with two open ends, this allows additional tiles to be placed along that long side. Some games require that a domino only be placed onto a chain that shows a certain number on both the left and right ends; other rules allow for a domino to be connected to chains with different numbers at both ends.
In addition to traditional dominoes, a variety of shapes and styles are available, such as curved lines, grids that form pictures when they fall, stacked walls, and 3D structures such as towers and pyramids. Artists who create these works of art, which are sometimes called domino art or domino sculpture, often use templates to guide their work.
When a domino is tipped, it causes the next piece to tip over and so on in a cascade of rhythmic motion. This has led to the phrase, “domino effect,” which describes a sequence of events that start out small but ultimately have much larger–and in some cases, catastrophic–consequences. Dominoes can be used in writing to convey this concept as well: a simple action, such as a character walking into a room or a character being pulled over by a police car, can trigger a series of events that change the course of a story.