A narrow, elongated depression, groove, notch, or slit, especially one for receiving or admitting something, as a coin or a letter. Also, a position in a sequence of morphemes that is not explicitly defined but has a specific grammatical function (see slot (disambiguation).

In the context of gambling, a slot refers to a machine in which coins or tokens are inserted to spin the reels and potentially win a prize. A slot machine may pay out winning combinations based on the paytable, or it may award an instant prize if the jackpot is reached. In either case, a slot is powered by a random number generator (RNG).

The RNG generates a unique sequence of numbers each millisecond, which corresponds to symbols on a reel. When the reels stop spinning, if the symbols align with the paytable, the machine will award a payout according to the paytable. In the case of online slots, this information is typically provided in the game interface or a separate menu.

Before the advent of electronic slots, the number of possible outcomes was limited by the physical limitations of the machines and the fact that each symbol could only occupy one stop on a reel. As manufacturers incorporated electronics into their machines, however, they were able to give each symbol a different weight on the screen, allowing them to appear with more frequency. This changed the odds of winning by giving the player more opportunities to hit the jackpot, or to activate other features such as bonus games.

Some casinos offer slots that accumulate a progressive jackpot. These machines maintain certain conditions or states that can be advantageous to knowledgeable players, such as a particular set of rules for collecting tokens and paying out a bonus when all ten have been collected. Knowledgeable players can identify these opportunities by monitoring jackpot levels and understanding the mechanics of their games. They can also be observant of the state of machines left by previous players.

Many people believe that it is important to switch machines after a short time, or when the jackpot has been hit, under the assumption that the machine will tighten up. This is a common misconception, as each spin of the slot is independent and has no correlation with previous results. Some slots, however, wiggle to make them more exciting to play, and some players have theorised that a wiggly slot is about to hit. This is not true, however, and it is recommended that players do not try to predict the outcome of a spin by watching the wiggles. They should instead focus on playing with the maximum bet to increase their chances of hitting a jackpot or triggering a bonus game.