A domino is a small rectangular block with a blank or patterned surface on one side and an arrangement of dots resembling those on a die on the other. It is the central piece in a game of dominoes, which is played with a set of twenty-eight tiles or more.

Dominoes are typically made of bone, silver lip ocean pearl oyster shell (mother of pearl), ivory, or a dark hardwood such as ebony with contrasting black or white inlaid or painted pips. The pips are usually small and square, although some sets of dominoes have rounded pips. They are also often engraved or painted with numbers or other designs, and some have the names of famous people inscribed on them.

The word domino appears in English as early as 1750, but it may have a longer history in French. Earlier, the word may have denoted a long hooded cloak worn together with a mask during carnival season or at a masquerade. The word may also have been used as a noun referring to the garment itself or the play, and later in reference to a large cape worn by a priest over his surplice.

Most domino games are played with two or more players. The rules of each game differ, but most involve forming a line of play by matching the open ends of adjoining dominoes. The open end of a domino is called its face, and the number of pips on its face determines its value and rank in the line of play.

When a tile is played, it is joined to the line of play in one of two ways: it may be placed adjacent to a double, with the dominoes touching at their matching ends; or it may be placed across the line of play, perpendicular to the double. If the domino is a spinner, it is added to the line of play with its matching side facing up.

After the dominoes are shuffled, each player draws a certain number of tiles from the stock according to the rules of the game being played. In most cases, the player with the highest double begins the first hand. In some games, however, the winner of the previous hand may make the first play, or the player with the heaviest single tile may begin the hand.

In the case of a tie, a new game is begun by drawing additional tiles from the stock until one of the players has a domino to play. This is known as breaking the tie.

A domino effect occurs when an event or series of events causes a change in another event or series of events. The change may be positive or negative. An example of a domino effect is the collapse of the Lehman Brothers bank in 2008. The collapse resulted in bank mergers and a bailout, and has had an impact on the economy worldwide. A domino effect can also occur in the social sphere, such as when someone loses a job and then finds it difficult to get a new one.