A narrow notch or groove, as in the keyway of a door or the slot for a coin in a vending machine. Also: a position within a group, series, or sequence; a place or position in a game or activity.

A machine in which players insert cash or, on ticket-in/ticket-out machines, paper tickets with barcodes to activate reels that spin and return combinations of symbols. These combinations award credits based on a pay table. Symbols vary from machine to machine, but classic examples include fruits, bells, and stylized lucky sevens. Most slots have a theme and feature symbols and bonus features aligned with that theme.

In computer science, a slot is the operation issue and data path machinery surrounding a set of one or more execution units (also called a functional unit). A slot is similar to a pipeline in dynamically scheduled computers, except that the relationship between an instruction and the pipeline to execute it is explicit.

In the case of online casino games, a slot is a dynamic placeholder that either waits for content (a passive slot) or calls out to the renderer to fill it in (an active slot). Slots are used in conjunction with scenarios and manage the display of dynamic items on the page. In general, a single slot can only contain one type of content. This means that if you use multiple scenarios to feed content into a slot, the results may be unpredictable.