A domino is a small rectangular wooden or plastic block with a line across the middle dividing it into two square halves. Each half has a number of dots, usually molded or drilled, that are called pips. A domino with all pips facing the same direction is called a double, and one with all pips facing the opposite direction is called a single. Dominoes are typically made of wood, but can also be made of ivory, bone or a composite material. Dominoes are available in both black and white, with either molded or hand-painted pips.

A large set of dominoes, carefully laid out in a sequence, can be a fascinating display. A domino is also a metaphor for how things can fall together in an unexpected and powerful way. A domino effect is a term for the way a chain reaction can spread from one person or group to many more people, often with significant consequences.

Dominos are used for a variety of games, and players take turns drawing from the stock (also known as the boneyard). When the highest double is played in a player’s hand, that player continues to play dominoes until he or she has a pair of matching tiles. The player then reveals the matching pair and plays them to establish an initial lead. The highest pair may be a pair of identical tiles, or a higher-value pair such as “six-five” or “six-four.”

When playing with dominoes, players are sometimes instructed to “play the first bone” in their hands. This is also known as setting, leading, or posing the bone. If a player is unable to play his or her first bone, the next highest bone in the player’s hand is played instead, and so on.

Depending on the game being played, a player’s hands may contain only seven dominoes. In these cases, the rest of the dominoes are left in a pile, called the boneyard, and do not participate in the game. This system is sometimes used to prevent cheating, as the remaining dominoes cannot be seen or counted.

The most common type of domino set consists of 28 tiles, each having either black or white pips on each end. This set is called a basic set. More advanced sets, such as double-nine, double-12 and double-18, increase the maximum number of pips on each end by three. However, such large sets are rarely seen in retail stores, as it becomes difficult to identify the number of pips on each piece.

Some dominoes are carved or painted with other symbols or designs, and others are engraved with Arabic numerals. They are also made from different natural materials, such as stone (e.g., marble, granite or soapstone); other hardwoods (e.g., ebony); metals (e.g., brass or pewter); and even ceramic clay or frosted glass.

Dominoes are more than just a toy or a game; they can be an important tool for teaching math and science. For example, using dominoes to help students understand the commutative property of addition can bridge the gap between moving the dots around with moveable manipulatives and writing equations in the classroom.