A slot is a narrow, elongated depression, groove, notch, slit, or aperture, especially a small one for receiving or admitting something, such as a coin or a card. It may also refer to:

A casino game that allows players to insert coins or paper tickets and receive a payout according to the combinations displayed on the machine’s reels. Originally, these machines used mechanical reels to display and determine results; however, by the mid-1990s, most had switched to a computerized system using a video monitor to show symbols and generate combinations. A standardized three-reel version became the standard, since it was less expensive to manufacture than older models. In addition to the reels, a slot machine usually has a credit meter which displays the current amount of money or credits the machine is holding. A jackpot meter may also be present, which lights up when a player has won the highest possible prize for that particular machine.

The theoretical hold percentage of a slot machine is calculated by the manufacturer at the time the software for that machine is written. The percentage is based on a number of factors including the reel strip settings, the maximum coin denomination, the pay schedule, and other information descriptive of the type of machine. In some jurisdictions, a slot machine’s theoretical hold percentage is required to be posted on the gaming floor.

In some casinos, a slot machine’s candle flashes to indicate that the machine needs service, is requesting a hand pay, or has a problem, such as a malfunction. In these cases, the machine must be taken to a designated service area or cage where an attendant can change the EPROM (electronic programming rom), which contains the machine’s operating program. The machine’s payout values are reprogrammed on the basis of this data.