A domino is a small rectangular block, about thumb-sized and normally twice as long as it is wide. Its face may be blank or have from one to six pips or dots. A complete set of dominoes contains 28 such tiles.

Normally, dominoes are played on a table with other dominoes, each player taking turns placing a tile on the edge of an existing one in such a way that the resulting chain of dominoes has a particular total value. The first player to reach this total wins the game. If a player cannot place a domino that would satisfy the requirement for the current chain, he or she “knocks” the table (or otherwise signals the other players to knock) and play passes to the next person.

Dominoes are also used to create artistic designs and structures that can be set up in a line or a grid, or stacked into 3-D towers or pyramids. These can have themes, such as cities or countries, or be made to resemble buildings or other real-world locations. Some designers use a domino design as part of a larger puzzle or game, such as a maze. Others simply want to show off their skill in creating a beautiful or unusual layout.

Many dominoes are made of plastic, though some sets are still constructed from wood and other natural materials such as bone, silver lip ocean pearl oyster shell, ivory, or ebony. These typically have a more attractive appearance and feel heavier in the hand than their polymer counterparts. They are more expensive, as well.

The most famous use of the term “domino effect” occurred during the Cold War when President Eisenhower cited it while explaining how Communism could spread from country to country, just as falling dominoes tumble over one another. The phrase has since come to be used to refer to any situation in which one small trigger causes a sequence of events that continue until the final event has been reached.

Lily Hevesh began collecting dominoes at age 9, and soon began constructing elaborate lines of them. She eventually started posting videos of her creations online, and now works as a professional domino artist. She has built setups that involve hundreds of thousands of dominoes, and some of her largest installations take several nail-biting minutes to fall after being triggered.

When teaching students about addition, an effective activity is to have them arrange a series of dominoes in a row and then write the sum of each. This activity helps students understand the commutative property of addition, and it is especially useful in helping younger learners grasp the concept. When using this technique, teachers should be careful to choose dominoes with clear numbers, and avoid ones that have the same color or pattern as each other. This will help prevent accidental mistakes that could result in the wrong number being added.