A narrow notch, groove or opening, as in a keyway in a lock or a slit for a coin in a vending machine. Also: a position in a group, series, sequence, or plan; a time or place for an event. She slotted the filter into the machine.

A machine that accepts cash or, in the case of “ticket-in, ticket-out” machines, a paper ticket with a barcode and a printed symbol on it, to activate reels that spin and stop to rearrange symbols. If the symbols match a winning combination, the player receives credits according to a pay table displayed on the machine or in a help screen. Pay tables vary by game and can be accessed through a ‘help’ button or ‘i’ on the touchscreen, and are sometimes included in the slot’s theme.

Slots, a system used by airports in the United States and around the world to limit aircraft takeoffs and landings at busy times, are helping to prevent delays and excessive fuel burn caused by too many flights trying to land or take off at the same time. The system is also helping airlines reduce their environmental impact by keeping planes on the ground longer and reducing unnecessary flying.