A slot is a narrow opening designed for something specific to fit through. A coin slot in a vending machine accepts quarters but not buttons or paper clips. A mail slot in a door lets letters pass through but keeps people out.

In scheduling, a time slot is a specific time period set aside for something. A doctor's office has appointment slots throughout the day. A TV network assigns different shows to different time slots. When you book a slot for something, you're claiming that particular window of time before someone else can.

As a verb, slot can mean to fit something into a tight schedule or space. If your teacher slots in an extra lesson before the test, she's squeezing it into the calendar. When puzzle pieces or parts slot together, they fit neatly into their designated spots.