Dominoes are small, rectangular blocks of a material such as wood or plastic with one or more groups of dots (often referred to as pips) on each side. The numbers or pips on each domino are used to mark the end of a line or pattern of play, as well as for scoring purposes. In general, a full set of dominoes contains 28 pieces. The word “domino” is also used to refer to the various games played with these blocks, including a series of positional games in which players place dominoes edge-to-edge against each other in such a way that the adjacent dominoes form either identical or a specified total.

Traditionally, dominoes have been made of silver lip ocean pearl oyster shell (mother of pearl), ivory or a dark hardwood such as ebony with contrasting black or white pip marks. Today, sets are available in a wide variety of materials. Some sets are molded from polymer clay or resin, while others are cast from ceramic clay or even stone. Most of these sets, however, have been designed to be as similar to the traditional European-style dominoes in both appearance and feel.

Before any game begins, the dominoes are shuffled and then placed face down on a flat playing surface. This arrangement of the dominoes is called the stock or boneyard. Each player draws the number of tiles permitted by the rules of the game from the stock. Once the player has a set of tiles he is able to play, he places them in a line called the layout or string. This line is usually centered on the open end of the last tile played. Depending on the rules of the game, some of these tiles may be doubles that can be played on all four sides or only two of their sides.

The first domino played in a line of play is called the lead. The players then take turns matching and laying down dominoes in such a way that the open ends of the matching pieces match those of the lead. The result is a line of dominoes that is called the string or line of play.

As the dominoes are matched and laid down, they begin to build up a chain reaction that ultimately results in the dominoes falling over. The energy from each domino as it is positioned against the next moves through the system, pushing it over like a neuron firing in the brain. This energy, which was potential energy, is converted to kinetic energy, the energy of motion. The energy then moves to the next domino and so on.

The word “domino” also has been used to describe an event or trend, especially a political or economic development that is expected to lead to a domino effect. In the 1950s and 1960s, it was used to describe a policy of containment of communism in Indochina, an approach that eventually led to the collapse of the Communist government in 1965.