A narrow opening, especially one through which something can be inserted or passed, as in a machine or container. A mail slot in a door, a time slot on a calendar. The etymology is uncertain, but it may come from the verb to slot, meaning to put into a space where it fits snugly. For example, a car seat belt slots easily into its slot.
In computers, a slot is a position in a memory hierarchy that contains a data item. A slot is usually assigned to a specific variable or attribute in the program, and it has an associated address and size. The size of a slot is usually determined by the length of a variable or attribute, and the address of a slot is determined by the name of the variable or attribute, which is placed in front of the address.
A slot is a dynamic placeholder that either waits for content (passive) or calls out for it (active). The content of a slot is dictated by a scenario using an Add Items to Slot action or by a targeter, and the presentation is specified by a renderer. In addition, some slots can have named attributes, and these are referred to as named slots. For example, a named slot can contain a class or a variable that is defined in a custom element. Airline slots are allocated to airlines based on a schedule that coordinates routes and optimizes flight times at constrained airports.