A slot machine is a gambling machine that accepts paper tickets or cash, and gives a payout based on combinations of symbols visible on the pay-line. Modern machines may have multiple lines and allow players to bet on several of them at once. Some have wild symbols that can substitute for other symbols and appear on every reel or a limited number of them. Some even have stacked wilds, which can cover entire reels. The slot machine’s pay table is listed on the face of the machine or within its help menu.

The sound that accompanies slot machine outcomes has been less well-studied than the visual aspects of the game, but one study found that players in a casino rated wins and LDWs more exciting when the machine was running at a faster speed with sound on, than when it was run at a slower rate with the sounds turned off (Loba et al 2001). The same experiment also showed that sound can serve as a secondary reinforcer and could in part explain the high rates of pathological gambling associated with slots play.

In electromechanical slot machines, a “tilt” was caused by the presence of a tilt switch that would either make or break the machine’s circuit. While modern machines do not have tilt switches, a tilt may still occur if the machine is tampered with, such as by an attempt to remove a coin from a coin tray or to remove a token from a token hopper. A tampered machine must be reported to the casino’s hard count team through use of the MEAL book.