A narrow notch, groove, or opening: a slot for a key; a slit for a coin in a vending machine. Also: a position, time, or place: He was slotted in at the front of the line.

In a slot machine, the player inserts cash or, in “ticket-in, ticket-out” machines, a paper ticket with a barcode and activates a reel-reeling mechanism to display symbols and determine winning combinations. The symbols vary with the theme of the slot, but classics include fruits, bells, and stylized lucky sevens. Most slots have a paytable that shows how much a player can win based on the number and value of symbols displayed on each reel.

With the advent of digital technology, some manufacturers have programmed their machines to weight particular symbols differently from others, increasing the likelihood of a winning combination on a given reel. They may also have multiple pay lines. This reduces the cost of a spin, but increases the odds of hitting smaller prizes.

The use of central flow management in airports is increasingly common, resulting in substantial savings in delays and fuel burn. But this approach will have limits. Eventually, it will be necessary to build new runways and airports with larger capacities, as well as to improve the efficiency of existing ones. This will require a substantial investment, and it will be difficult to find enough slots for the planned growth. Even so, the benefits of a more efficient aviation system will be significant.