A slot (plural slots) is a narrow aperture or groove in something, often used to allow it to fit into a larger whole. Unlike the more common word hole, which is the space within a wall through which a door or window can be opened, a slot is usually rectangular in shape and wider at one end than the other.
In online casino games, a slot is a dynamic placeholder that either waits for content to be added (passive) or can be directed by a scenario to fill in its contents with a list or other type of object (active). Slots work in tandem with scenarios and renderers.
A player inserts cash or, in ticket-in, ticket-out machines, a paper ticket with a barcode, into the machine, and activates it by pressing a lever or button (physical or on a touchscreen). The reels then spin repeatedly until they stop, and matching symbols on the payline determine whether and how much a player wins. The amount of money the player can win varies between different types and versions of slot machines, from classic 3-reel ones to more modern 5- or 7-reel options. Many slots have a theme, with symbols and bonus features that align with the concept.