Domino is a small rectangular wood or plastic block with a blank or slightly patterned face on one side and a row of dots resembling those on dice on the other. It is used in games involving a line of dominoes, where the first domino is tipped over by another player, causing it to trigger more and more dominoes to fall until all are completed. This has led to the use of the term in general to describe a chain reaction or cascade that starts with one action and leads to much greater, often catastrophic, consequences.

Dominos are usually played by two players, but many variations of the game exist. Typically, a double-six set of 28 dominoes is used, although larger sets are available. Players take turns drawing tiles from a boneyard, called the stock or boneyard, and placing them on their side of the board. Then they set up a line of dominoes, with each player taking turns to play their tile.

Each domino has a number of dots that correspond to the suit (e.g., spades, hearts, diamonds) in which it belongs. It is possible to create a domino with only one particular suit, but this is rare. The most common types of domino games involve layouts, in which the first domino is tipped over, and other dominoes are placed so that they form a straight or curved line and then fall.

In addition to the traditional lines, many players create domino art that features curved lines, stacked walls, or grids that produce pictures when the dominoes are tipped over. The goal of this type of domino art is to make a pattern that will impress viewers or make the viewer think about how the piece was made. When creating these types of domino art, the player must consider the amount of force that will be needed to knock over the design.

For example, if the curved line is set up so that it will be forced over by a force from one direction, that force must be greater than the total weight of all the dominoes in the layout. This is why some designers of domino art prefer to use a scale model of their finished design before they actually build it.

When creating these designs, the player must also consider the number of dominoes involved and the size of the space in which it will be set up. This is important because a domino with too few or too many tiles will not have the same effect as a design with just the right number of tiles.

The word domino is also used to refer to the game itself, and some players collect a large collection of dominoes for this purpose. Other uses of the word include the idiom domino effect, in which a small event can lead to a large consequence, and the term for a hooded robe worn with an eye mask at a masquerade.