A slit or other narrow opening, especially one for receiving something, as a key in a lock, a coin in a slot machine, or a hole in an airplane wing used for attaching a device to control the plane’s flight. Also:

A position or place in a group, sequence, series, or list; a spot or position of employment.

In computer programming, a software element that defines an interface between a program and the operating system for loading dynamic information on a Web page. The slots in a Web page are filled with content either by a user action that calls for or accepts a repository item, or by a renderer that specifies how the information should be presented on the page.

A passageway between the rails on a street-railway through which the grip on a car passes to connect with the traveling cable. Also:

An area in a field, game, or track where a deer has been walked or tracked by scent or footprints. Also:

On a video game, a space on the screen for a character to move into, often indicated by a dotted line or a flashing arrow. Also:

The slot on a machine through which cash or, in “ticket-in, ticket-out” machines, a paper ticket with a barcode is inserted to activate the reels and award credits based on combinations of symbols that appear on the pay table. Symbols vary with the theme of the machine, and may include classic icons such as fruits, bells, and stylized lucky sevens. Many slots have a maximum cashout amount, which is listed in the game’s properties.

In etymology, a slot is a recess or hollow, and the word is derived from the Middle French noun esclot, which in turn is probably from Old Norse slod (“track”). As a verb, to slot means to make a slit or groove, or to insert into a slot.

You’ve checked in on time, made it through security, found your gate, queued to get on board, struggled with the overhead lockers and settled back into your seat – only to hear the captain say, “We’re waiting for a slot.” So what is a slot, and why can’t we take off as soon as we’re ready? Let’s dive in and find out.