A slot is a narrow opening or groove in something. It is also the name of a place in hockey referring to the area right in front of and between the face-off circles in the offensive zone.
A player inserts cash or, in ticket-in, ticket-out machines, a paper ticket with a barcode, into a designated slot on the machine and then activates it by pushing a lever or button (either physical or on a touchscreen). When the reels stop spinning, if the player matches symbols in a winning combination according to the pay table shown on the machine, he or she wins credits based on the amount that he or she bet before. Depending on the game, the symbols may be classic objects such as fruits or bells, stylized lucky sevens, or themed characters that fit the game’s theme.
Before microprocessors became ubiquitous, slot machines were all-or-nothing affairs: if you yanked the lever, either cherries or stylized lucky sevens lined up and you won some money, or they didn’t and you lost everything. The advent of better computer technology gave casinos the ability to offer higher jackpots and more exciting games while precisely controlling percentage payback and odds.
The probability that a particular symbol will appear on a pay line is determined by the number of virtual stops and how the winning symbols are weighted. A win is only a probability, however, and the player must know what his or her chances are to make informed bet decisions. That is why the casino shows the player how much a winning line is worth and what the specific symbols are.