A narrow notch, groove, or opening, such as a keyway in a piece of machinery or a slit for a coin in a vending machine.

A slot is also a position in a group, series, sequence, or set. (From Webster’s New World College Dictionary, 4th Edition)

A slot is the narrow space in a slot machine where coins are placed. Originally, slots were designed as a diversion for casual gamblers, and they quickly became the most popular game in casinos. Today, slot machines generate more than 60 percent of casino profits in the United States.

In a traditional mechanical slot machine, a player pulls a handle to rotate a set of reels (typically three) with pictures printed on them. When the pictures line up with a pay line, the player wins — or loses. Typically, the more you bet, the higher your chances of winning.

Modern slot machines still look like the old mechanical ones, but they operate on a different principle. With microprocessors inside, manufacturers can adjust the odds of a given sequence by changing how many virtual stops correspond to each reel. This allows a machine to appear to be “close” to a winning symbol, even though the odds are actually much lower.

Digital technology has also introduced new kinds of slot games. Some are based on specific themes, such as television shows or horse racing. Others are based on gambling, including poker, blackjack and craps. Some are free and run on virtual money, while others require players to deposit real cash to play.