A slot is a narrow notch, groove, or opening, as in the keyway of a lock or a slit for coins in a vending machine. Also, a position in a group, series, or sequence; a place or time for an event.
In its earliest days, a slot machine required you to insert coins and pull the handle to spin the reels. You then crossed your fingers and hoped for a winning combination, which would appear on a payline across the center of the reels. In the 1950s electromechanical machines introduced new payout schemes, including 3- and 5-coin multipliers. By the 1970s video slots, which simulate reels on a monitor, replaced traditional mechanical machines.
Modern slot games use random number generators (RNG) to generate a string of numbers each millisecond, which determines the symbols that land and how much you win or lose. They are calibrated in advance to hit a particular percentage of the money put in, and they are tested over millions of spins to ensure that the actual returns match this figure. The variance of a slot, however, is harder to predict; low volatility slots tend to pay out often but have smaller wins, while high volatility slots can be risky but offer larger (though less frequent) payouts.
Most slot games have a theme, and the symbols and bonus features are aligned with this theme. Classic slots usually have 3 or 5 reels and follow the standard 25-payline structure. Online slots, on the other hand, are more versatile and can feature up to 1024 ways to win. Several software developers have even created slots that use characters from hit movies and TV shows.