A domino is a small rectangular wood or plastic block, usually about the size of a thumb, with one side blank or marked by dots resembling those on dice. It is normally twice as long as it is wide, which makes it easier to re-stack the pieces after use. The value of a domino – sometimes also called its rank, or weight – is determined by the number of pips on the two adjacent ends. In the most common variant, each end has a value of six pips, although in some games each end may be a different value. A domino is said to be “heavier” than a “lighter” one with the same number of pips.

There are a large number of domino sets in use throughout the world and a wide variety of games can be played with them. The most widely used set in the West is the double-six set, though games can be played with smaller sets as well.

Each player draws a set of dominoes from the stock and then positions them on the table with their matching sides touching, so that a chain of dominoes is gradually built up. The first player, whose turn it is, places the first domino tile onto the table – normally a double – and then continues to play tiles in a sequence that reaches the desired end of the chain. The value of a single tile is determined by its position in the chain, and a player can only place a domino with an adjacent end that has either a number that is useful to him or a number that forms a desired total.

Dominos are also popular in construction projects and have been used to build structures such as houses, towers and bridges. They can be arranged in a linear fashion to create straight lines, or in curved and angular patterns. They can even be stacked in 3-D to form pyramids and other structures.

The term domino is often used to refer to a person or event that can have an impact on others in the same way as falling dominoes. This impact can be positive, negative or neutral and is sometimes referred to as a domino effect. For example, a person who has a mental health problem that is not treated could affect the lives of their friends and family in a similar way to how a domino effect would occur if they had a car accident or suffered a serious injury.

In the game of domino, players score points by awarding the number of pips on their opponent’s tiles to the winner (a 6-6 count as six; a double-blank as zero). The player who scores the most over the course of a given number of rounds wins the game. A player can also win by being the first to reach a predetermined target score, such as 100 or 200 points. Other rules for scoring vary among games.