The word slot has many meanings, but the one most associated with casinos is a machine that accepts cash or paper tickets with barcodes. Players insert the ticket into a slot on the machine and then press a button (either physical or virtual) to spin the reels. If the symbols line up on a payline, the player receives credits based on the pay table. Some slots have a single pay line, while others have multiple.
In the past, the number of symbols on a reel was limited by the number that could fit on a physical reel, so manufacturers weighted particular symbols to increase their chances of appearing. This was done by assigning each symbol a different probability of appearing, and then using the odds of each symbol to calculate how often it would stop at a blank or a paying position on a particular reel. This made it easier to win large amounts of money, but also diluted the jackpot sizes because winning symbols appeared less frequently.
The random-number generator that determines which symbols appear on the reels operates continuously, running thousands of numbers every second. When it receives a signal, such as the button being pressed or the handle pulled, the computer checks to see if any of the numbers correspond to a specific symbol. If it does, the computer stops the reels at those positions. If not, it continues generating random numbers until a match is found.