A slot is a narrow opening, especially one for receiving something, such as a letter or a coin. It is also a position or place in a schedule or series.

In slot machine games, a player spins the reels and hopes to hit a winning combination of symbols on a payline. The symbols are determined by a random number generator (RNG) following an algorithm that cycles thousands of numbers each second. In a physical machine, these symbols are represented by mechanical reels that stop when a specific pattern is reached.

As computers became more advanced, manufacturers began to use multiple reels, and the number of possible combinations increased dramatically — with five physical reels containing 10 symbols per reel, there are 103 = 10,000 possible outcomes. However, this still limited jackpot sizes as winning combinations would occur very rarely. In the 1980s, manufacturers incorporated electronics into their machines and programmed them to weight particular symbols.

When the machine weighed these symbols, the odds of hitting them were significantly increased. This led to the development of video slots, where players interact with a video screen instead of spinning physical reels.

At an airport, a slot is the right to operate at a certain time, granted by EUROCONTROL as part of its Air Traffic Management role. It allows airlines to save on delay payments and fuel costs by not flying unnecessarily, and thus helps reduce the amount of CO2 emitted into the atmosphere.