A slot is a position within a group, series, or sequence. It can also refer to a position of employment or to an opening in a structure, such as a door.

In casino gambling, a slot is a machine that pays out credits according to a pay table when certain combinations of symbols appear on a pay line. Players insert cash or, in ticket-in, ticket-out machines, paper tickets with barcodes into the slots and activate them by pressing a lever or button (physical or virtual on a touchscreen). The reels then spin and stop to reveal a combination of symbols. Credits are awarded based on the pay table, which is displayed either above or below the slot machine’s reels. The pay table is typically aligned with the machine’s theme.

With the advent of microprocessors, the computers inside modern slot machines can assign a different probability to each symbol on each reel. This allows manufacturers to make it seem that a winning symbol is “so close”, even though the odds of such a symbol appearing are very low.

Psychologists Robert Breen and Marc Zimmerman found that playing video slots causes people to reach a debilitating level of involvement with gambling three times more rapidly than those who play traditional casino games such as blackjack or roulette. Their research used Power-lab systems to amplify the electrocardiogram (ECG) signals produced by players’ hearts as they responded to slot machine sounds.

In aviation, a slot is an allocated time and place for aircraft to take off or land at an airport, provided that the air traffic control system has the capacity to manage it. The use of slots has led to substantial savings in delays and fuel burn as well as significant environmental benefits.