A slot is a narrow notch, groove, slit, or opening, especially one in something used for receiving or admitting something, such as a hole for coins in a machine. It is also the term for a position in a program or schedule: Visitors can book a time slot a week or more in advance.

In the United States, private ownership of slots is legal in Nevada and a number of states allow casinos on riverboats or permanently anchored barges. On military bases, slot machines have caused a great deal of controversy because they are considered gambling devices and not a legitimate means to raise funds for the military. Additionally, many servicemembers use them to spend money they have earned in other ways, leading to a great deal of gambling addiction and financial problems.

Psychologists have studied how slot machines influence gamblers, and have found that players tend to lose more frequently on losing machines than they win on winning ones. They believe that this is because they are influenced by a psychological phenomenon known as conditional reinforcement, in which the audio-visual stimuli associated with winning on a slot machine acquire a reinforcing value, encouraging people to continue to play, despite their losses. This may be exacerbated by the fact that most slots are designed to accept only a certain number of coins, making it easy for people to exceed their bankroll. Despite these concerns, slot machines remain popular, and many casinos offer multiple types of games.