A slot is a dynamic placeholder that either waits for content (a passive slot) or calls out for it (an active slot). It encapsulates reusable logic, such as data fetching, pagination, etc. The slot also delegates some of the visual output to the renderer, via scoped slots. Slots work in tandem with scenarios and renderers: a scenario specifies the contents to be displayed in the slot, while a renderer determines how that content is presented.

Slots are often characterized by their volatility, which is an indication of how risky or safe a slot is. Low-volatility slots tend to pay out more often, but the wins are smaller in value. Conversely, high-volatility slots are more risky, but they pay out larger amounts when they do hit.

A slot is a narrow opening or groove, especially one that is used to hold a pin or key. The term can also refer to a position in a series or sequence, such as an airport slot that grants an airline the right to fly at certain times, or a place in the lineup for an ice hockey game. In computerized slot machines, a player inserts cash or, in ticket-in, ticket-out machines, a paper ticket with a barcode into the designated slot and activates it by pressing a button or lever. The slot then displays a series of reels, with symbols appearing on them and the goal being to line up matching ones along pay lines.