A slot is a narrow opening or groove in something. It can also refer to a time in a schedule or program: “Visitors can book a slot for a tour next week.” A computer has many slots that hold data and programs.
A slots game is a machine that pays out credits based on combinations of symbols that line up in the pay line (or certain single images). You insert cash or, in “ticket-in, ticket-out” machines, a paper ticket with a barcode into the slot to activate the machine. Then you pull a handle or push a button, either physically or on a touchscreen, to spin the reels and arrange the symbols. The pay table tells you what each symbol is worth and the number of credits you can win if they line up. Most slots have a theme, and the symbols and bonus features reflect it.
When a slot doesn’t pay out, it’s called cold. When it does, it’s hot. These terms stem from electromechanical slot machines’ tilt switches, which would break or make a circuit when the machine was tilted, tampered with, or otherwise malfunctioning. Modern machines don’t have tilt switches, but a glitch in the logic that governs their operation (door switch in the wrong state, reel motor failure, paper out) can cause them to malfunction and stop paying out.
As technology has improved, so have the bonus rounds in slot games. Typically, they involve a free spins round or some other kind of interactive game like a mystery pick game. These add-ons are fun, but they can also lower the odds of hitting a big payout. Keep this in mind as you play: The more complicated a game, the worse your odds are.