A slot is a thin opening or groove in something, such as one used to mail letters. The word is also used as a verb meaning to put into a position within a series or sequence: “He slotted his ideas into the theory.”
Charles August Fey invented the first modern slot machine in 1894, which had a lever that set the reels spinning when pressed and playing card suitmarks that lined up to form poker hands. The machine was a hit at a San Francisco saloon and became wildly popular, spawning similar machines across the country. By the 1920s, however, illegal operations and widespread public fear led to stricter gambling laws and eventually prohibition outside of Nevada by 1951.
After placing a bet, players press the spin button (or pull a lever on older machines) to start the reels spinning. When they stop, the symbols will align in a random combination, which determines whether the player wins. Some machines have multiple pay lines, while others have a single, visible line that awards credits depending on the combination. In addition, some symbols are wild and can substitute for other symbols to complete winning combinations.
The payout values for each symbol are listed on the machine’s pay table, which is typically displayed above and below the area where the reels spin. The odds of a specific combination appearing are calculated by multiplying the probability of each individual symbol by the number of stops on the reel. In a mechanical machine, these probabilities are calculated using a complex set of gears and rods; in an electronic machine the information is stored in microprocessors.