A domino is a small rectangular tile, often made of wood or plastic, with one side bearing an arrangement of spots or dots that resemble those on dice. The opposite side of the domino is blank or identically patterned. The domino is used as the foundation for a variety of games, including poker and blackjack. A game of dominoes can be played by a single person, with two or more players, or in teams.

In many domino games the players build chains or structures of tiles by placing them edge to edge against each other. The tiles must be placed so that the value of the numbers on both ends of a particular tile (or domino) matches or exceeds the value of a previous tile in the chain. Hence, the tiles are said to be “matched” or “matched up.” The players continue building the chains until they reach a target score, or until it becomes impossible to place any more tiles.

Dominoes can be played with any number of players, although the fewer the players, the easier the games are to play. A typical domino set consists of 28 tiles. The most common domino is the double-six, with a total of six numbers from 0 (or blank) to 6. Each domino has a line down the middle that divides it visually into two squares, each of which can be numbered. The most common domino has the same pattern on both sides, so each side is valued as equal, but some sets have different patterns on each half of the domino.

Most dominoes have a rounded top and a flat bottom, so they can be stacked in rows. A specialized type of domino has an octagonal top and a round or slanted bottom, to allow it to fit into a circular or square hole in another piece. These special dominoes are often used to create large layouts for a game, such as a domino pyramid.

Each player draws a set of dominoes, either by chance or by drawing lots. The first player begins by putting the first domino on the table, usually with the double-six (although other starting tiles may be used). Then each player plays his or her tile, positioning it so that the number on the end of the tile corresponds to the total value of the previous tiles in the chain.

When the first domino falls, it generates a potential energy that can be tapped into to cause other dominoes to fall. The energy is converted into friction between the top of the domino and the bottom of the next domino, and also into sound and heat. The next domino then picks up the momentum of the fallen first domino, and so on, in a sequence that can extend hundreds or thousands of pieces. A chain reaction of this kind is a lot like a car crash or rocket launch, although it’s much less exciting to watch.