We’ve all been there: You’re at the airport, check in is smooth, you make it through security and find your way to the gate just in time for boarding. You get your seat and settle in. Then the captain announces that your flight will not take off until they can “find a slot.” What is a slot? And why can’t the plane leave sooner?

In the context of casinos, a slot is a position on the machine that’s designated for you. Players insert cash or, in the case of ticket-in/ticket-out machines, paper tickets with barcodes into slots that activate reels that display symbols and pay out credits based on a combination of rules. The symbols vary from game to game, but classics include fruits, bells and stylized lucky sevens. Most slots have a theme, which guides the design of the symbols and bonus features.

The weighting of the symbols on a reel changes with each spin, making some more likely than others. This is why you might think you’re so close to a JACKPOT on the second reel, but the third one seems to come up blank. The truth is the odds are actually lower for the third than for the first two.

Another helpful tip for playing slots is to choose machines that have shown a recent win. At brick-and-mortar casinos, this is usually displayed by showing the number of credits left on a machine and the amount of money it has cashed out recently. The higher the amount of cash out, the better the chance that the last player left a winning slot behind.