A domino is a flat, thumb-sized, rectangular tile that bears an arrangement of spots or dots, or blank spaces, on one side, and has a line or ridge that separates it into two parts. Twenty-eight such tiles constitute a complete set of dominoes. Dominoes are used in a variety of games, the most familiar being a simple game where players place their dominoes on a table in long lines and then knock over all those on adjacent sides. The term “domino” is also applied to a game that is played by arranging pieces in a grid or other pattern and then using them to make combinations.

Dominoes were invented in China in the 1300s and are cousins to playing cards. In addition to being a great way to pass the time, they can be used to create impressive displays of stacked dominoes that form pictures or resemble walls. Some of these designs use curved lines, grids that form words or numbers and even 3D structures like towers and pyramids.

Generally, dominoes are arranged in a line on a table, with each player drawing a number of tiles. Once each player has drawn their tiles, the first tile placed on the table is determined by drawing lots, or by who holds the heaviest hand. All subsequent tiles are then positioned with their faces against each other in a row. The dominoes remain in this position throughout the hand or game until all have been flipped over and their values revealed. This collection of flipped-over tiles is known as the boneyard.

Each domino has a specific value according to its type. The value of a double is usually half of the total of the number of pips on all its edges, and the value of a 0 suit domino is zero. These values are important in the different types of domino games.

The first domino in a line is called the starting domino and it can only be knocked over by another domino that has its own number of pips on the end. Each domino in a line is connected to the next domino by its own matching pair of ends. The connecting ends of each domino are called the open or unused ends. Depending on the game, additional tiles may be added to the domino layout to increase its number of unused ends.

The simplest domino sets only contain 28 dominoes, which are sufficient for most games with two to four players. More extensive sets, including double-nine and larger, exist for players who are interested in longer domino games. These sets have progressively increased maximum number of pips on an end and therefore the total possible combination of dominoes. These extended sets are often made from more luxurious materials such as silver lip ocean pearl oyster shell (mother of pearl), ivory, or ebony, with the pips inlaid or painted onto them. Other types of materials for dominoes include marble, granite, soapstone and other woods; metals; or ceramic clay.