A slit or opening for receiving something, such as a coin or letter. Also: a position in a group or series of events, or a job or assignment

A slot is the smallest available unit of a game that can be occupied by a symbol. The number of symbols available in a slot depends on the type of machine. Different games have different rules for filling slots, but they all depend on a random number generator (RNG) to determine the positions of symbols on each reel. A player presses the spin button, and the RNG generates a set of numbers that correspond to each possible combination of symbols. When a winning combination appears, the player receives the prize.

Historically, the first slot machines were based on poker card games. In 1891, Sittman and Pitt created a machine that allowed players to insert a nickel and pull a lever to spin five drums holding 50 card faces. If the card faced up, the player would win a fixed amount. The Liberty Bell machine invented by Charles Fey in San Francisco in 1899 used a similar concept.

Modern slot machines are designed to appeal to a younger generation of gamers by using video monitors and 3D graphics. They also have more varied bonus rounds and group competition, and they are often branded with pop culture personae to attract the attention of teenagers. Psychologists have noted that video slot machines can lead to gambling addictions just as quickly as other casino games.