A slot (or slit) is a narrow opening, often a passage, for receiving something, as a coin or letter.
The term slot is also used to refer to a position in a queue or line-up, such as for a job or a bus seat. In the United States, a slot machine is a gambling machine that takes coins or paper tickets with barcodes and gives out credits according to a predetermined schedule. Slot machines are the most popular form of gambling in casinos and account for more than 60 percent of casino profits.
Although the technology behind modern slots has changed, the basic idea is the same as the old mechanical models. A player pulls a handle to rotate a series of reels with pictures printed on them, and the winning or losing combination is determined by which symbols line up with the pay line (certain single images are sometimes winners as well). The amount of the payout depends on how many matching symbols stop along the pay line.
Until the 1990s, players dropped coins into slot machines to activate them for each spin, but in online casinos, advance deposits and credit meters make this largely unnecessary. In addition, most electromechanical machines had “tilt switches,” which would make or break a circuit when they were tilted, but modern electronic slot machines have no such switch, so the random-number generator that picks the combinations remains unbiased. It is only possible to beat a slot if you know the code and can hack into its system.