A narrow notch, groove, or opening, as in a keyway in a piece of machinery or a slit for a coin in a vending machine. (slang) To put something in the slot where it belongs.

Traditionally, players insert cash or, in “ticket-in, ticket-out” machines, paper tickets with barcodes into the slot at the top of the machine and pull a handle to activate a series of reels that spin and stop to rearrange symbols. If the pictures line up with a pay line, the player receives credits according to a payout table. Depending on the type of machine, the symbols may include fruits, bells, stylized lucky sevens, or other themed items.

Conventional mechanical designs gave way to electrical machines with more sophisticated money-handling systems and flashier lights, but the basic principles of the game remained the same. Charles Fey’s 1887 invention allowed for more frequent payouts and used a different symbol set, including diamonds, spades, horseshoes, hearts, and liberty bells—three aligned liberty bells signaling a jackpot.

Today’s electronic machines use random number generators to assign a combination of numbers to each possible stop on the reels. When a machine receives a signal, whether from the button being pressed or the handle being pulled, the computer sets a number and the reels stop on that combination. Between signals, the computer continues to run through dozens of combinations per second. So, if you see someone win a huge jackpot and think it should have been yours, don’t fret: It just wasn’t your time.