You checked in on time, made it through security, found your gate, queued to get on board and struggled with the overhead lockers before settling back into your seat. But then you hear the captain say: “We’re waiting for a slot.” What is a slot, and why can’t we take off as soon as we’re ready?

A slot is a narrow notch, groove or opening. It could be a keyway in a piece of machinery, a slit for a coin in a vending machine or the space that a car seat belt slots into easily. A slot can also be a position in a group, series or sequence.

In football, a slot receiver lines up in the area between and slightly behind the outside wide receivers on the offensive team. They are usually a little shorter and faster than traditional wide receivers, and they excel at running precise routes. They can also be effective blockers, especially if they have good chemistry with the quarterback.

Slots are also used to manage air traffic at very busy airports, and they help reduce the long delays that can occur when too many flights try to take off or land at the same time. This is known as central flow management, and it has been hugely successful in Europe, with significant savings in both delays and fuel burn. This method is now being used around the world.