The first and most obvious feature of a slot machine is the reels. The reels of a slot machine have one or more active lines. When a player triggers the lever, coins, or button to activate the game, a series of symbols spins around on the reels. When a combination of three or more of the same symbols appears, the player is awarded credits based on the paytable. Depending on the theme, the symbols used in a slot game may vary. The most common, traditional symbols include fruit, bells, and stylized lucky sevens. The number of combinations is largely determined by the number of active lines, or paylines.

A slot is a narrow hole or opening in a machine. Usually, the coin is dropped into the slot and tripped the mechanism or the cylinder. Some of these cheating strategies are obvious, but others are less obvious. These cases led to the creation of more secure coin acceptance devices. Most modern slots now accept paper currency, tickets, and other forms of currency in addition to coins. While the use of coins in slot machines remains illegal, it is not uncommon to see slot machines in public areas.

A slot has a grammatical function. A slot fits any morpheme sequence in any grammatical context. For example, a copy desk can have an interior opening that is occupied by the chief copy editor. A plane can be assigned to a slot on an airplane by an airport or air traffic authority. A coin can be inserted into the slot and placed in the machine. Then, the coin is spun.