In casinos, a slot is a position on the betting line or table that can be reserved. Slot machines once had a reputation as arcade games only played by little old ladies, but today they account for 85 percent of casino profits. To keep their customers hooked, the makers of these machines have drawn on a dizzying array of psychological insights to make them look and feel more addictive.

The first modern slot machines used revolving mechanical reels to display and determine results. But those systems were limited to 103 = 1,000 possible combinations, which severely restricted jackpot sizes and overall payouts. The advent of microprocessors made it possible for manufacturers to “weight” particular symbols, giving them a higher probability of appearing on a payline than they would have had on a physical reel.

When you play a slot, you insert money (or, in ticket-in, ticket-out machines, a paper ticket with a barcode) into the machine and activate it by pressing a button or lever. The reels then spin and stop to rearrange the symbols. If the resulting combination matches one on the paytable, you receive credits based on the size of your wager. Many slot games have a theme, with symbols ranging from traditional fruit and bells to stylized lucky sevens.

When you fly, you’ve checked in on time, cleared security, found your gate, queued to get on board and settled into your seat only to hear the captain say, “We’re waiting for a slot.” What is a slot?