A slot is a narrow opening or groove in something, such as the one you might put coins into to make a machine work. If you slot something into something else, it means that you fit it into its proper place, such as a CD into a player or the seat belt into the buckle of your car. You might also use this term to refer to a time slot in a schedule or program.
The Slot receiver gets his name because of where he typically lines up on the field during pre-snap motion and for running plays. He is usually positioned between the last lineman and the outside wide receiver and must have great speed to catch passes from the quarterback and run routes, as well as evade tackles when blocking for other players.
In the past, many casinos used a single payline on their slot machines and only paid out when all symbols lined up. However, when slot machines switched to electronics and computer chips, it became possible for symbols to occupy multiple spaces on the reels. This made it much harder to achieve high jackpots and increased the odds of losing. In order to make up for this, the manufacturers started to weight certain symbols more heavily than others. This meant that you could bet a single penny but still end up wagering far more per spin than you intended. This is why it is vital to read a slots pay table carefully and to understand the mechanisms of the machine before playing.