Domino is a tile-based game that combines strategy, chance, and spatial reasoning. It is played by a single or more players, and requires a large flat surface such as a table or the floor. It can also be played on a specially designed board, which adds to the challenge of the game.

Dominoes are typically twice as long as they are wide, and their faces feature a series of dots called pips that range from six to none or blank. Each domino has a value that is indicated either by the number of pips on its face or by a combination of numbers on its sides, known as its rank. When a domino is played, its potential energy converts to kinetic energy and some of that energy is transferred to the next domino in line, pushing it over. This process continues until all of the dominos are down.

The word domino and the game itself appeared in the mid-18th century, probably in France, though the origin of both is unclear. It is possible that the word derived from an earlier sense of the word, denoting a long hooded cloak worn together with a mask at a masquerade or carnival, or perhaps from a reference to the contrasting black domino pieces against a white surplice used by priests.

When a domino is placed in a domino layout, it must be matched with a tile that has the same value on its two adjacent ends. The ends of a domino are often called open, and additional tiles can only be played onto the ends of a domino that have an opening for them. This allows the domino chain to develop a shape that suits the needs of the particular game being played.

In addition to the traditional European-style domino set made from bone, ivory, silver lip ocean pearl oyster shell (mother of pearl), or ebony, many sets have been made from a variety of other materials including stone (such as marble, granite, or soapstone); other woods, such as ash, oak, or redwood; metals like pewter or brass; ceramic clay; and even frosted glass. These sets often have a more unique appearance and are sometimes more durable than their polymer counterparts.

Most domino sets contain double-nine dominoes (91 tiles), although extended sets containing larger numbers of pips are available. It is possible to create a larger domino set, but it would be impractical for most games to use it in practice. A domino set can also be modified by adding additional tiles to the layout, increasing the maximum number of pips on any end. This is done to extend the number of combinations of tiles that can be laid down and thereby the number of possibilities for a game. This is often done by gluing on extra pieces of the same rank and color. This makes the domino set more visually appealing and can make it easier to play certain types of games.