A slot is a slit or narrow opening, especially one for receiving something, such as a coin or a letter. In computing, a slot is a container for dynamic items on a web page; they can be either passive (waiting for content to appear) or active (calling out for content to fill them). Slots are used in conjunction with scenarios, which specify the content to add to the slot, and renderers, which decide how to present that content to the user.

In gambling, a slot is the designated position where coins or paper tickets with barcodes can be inserted. Activation of the machine typically occurs when a player pulls a lever or pushes a button (physical or on a touchscreen). The reels then spin, and if matching symbols appear on a payline, the player earns credits according to the machine’s paytable. Most slot games have a theme, with classic symbols including fruit and stylized lucky sevens.

Historically, casinos used a limited number of symbol positions on each reel, which capped jackpot amounts and the number of possible combinations. However, manufacturers soon incorporated microprocessors into their machines, allowing them to weight particular symbols with greater probability than others. This gave the impression that winning symbols were appearing far more often than they actually did, limiting jackpot sizes and frequency of payouts.

A slot is also a term for a position within a group, sequence, or schedule. For example, I booked my haircut for the 2 p.m. slot. In aviation, a slot is an allocated time and place for a plane to take off or land, as authorized by the air-traffic control service.