A slot is a hole, slit, or aperture, especially one that receives or admits something. It is also a position or job, such as the slot occupied by the chief copy editor in a newspaper. From Farlex English Dictionary:
Originally, electromechanical slots had reels and a lever that operated the machine when a player pushed the button. Now, the majority of slot machines are digital and use a random number generator (RNG) to determine the position of symbols on each reel, and thus the paylines. Some modern slot machines even allow players to adjust the frequency of these random numbers, allowing them to control their chances of winning.
The odds of a symbol appearing on a payline are determined by the weighting of that particular reel; higher-paying symbols tend to appear more often than low-paying ones. However, because the reels spin independently, the same symbols may occupy several stops on each of the reels, which distorts the overall odds.
Although most people enjoy gambling and do not experience serious problems, a small subset of gamblers can suffer from significant harms related to the game, including financial debt, interpersonal and professional difficulties, and even involvement in criminal activities to support their habit (Blaszczynski, Sharpe, Walker, Shannon, Coughlan, & Lahn, 2005). The allure of slots is thought to be rooted in arousal and the anticipation of rewards.
In addition to their enticing nature, slots are also associated with an absence of auditory and visual feedback. This combination of exogenous reining-in of attention and the arousal generated by the game results in an unusual state for many slot machine players – one that Dixon and colleagues call dark flow.