A slot is a narrow opening into which something can be inserted. It is also the name of a place in a schedule or program. People can reserve a time slot for an activity online. If something slots into another object, it fits into it easily. For example, a car seat belt slides into the buckle easily.

Historically, slot machines used mechanical reels that displayed a number of symbols on each reel, and each symbol had a different probability of appearing. When a winning combination of symbols lined up on the pay line, the machine paid out credits based on the payout table. The number of possible combinations was limited by the physical structure of the machine and the speed at which the reels turned.

Modern slot machines use microprocessors to assign different probabilities to each symbol. This allows them to create a wide variety of outcomes, and to increase jackpot sizes by weighting particular symbols. A symbol might appear only once on the reel that is displayed to the player, but it might occupy several stops on multiple physical reels.

In addition to increasing the size of the payouts, modern electronic slot machines have several other features that attract players. These include progressive jackpot levels, free spins, and bonus rounds. Many also have a theme. These themes can be a movie or game, and they often include symbols that reflect the theme. For example, a movie-themed slot might feature stylized lucky sevens. Some slot machines also offer multiple jackpot levels, which can make them more exciting to play.