An airport terminal is a building at an airport where passengers transfer from ground transportation to the facilities that allow them to board airplanes.
Passengers taking a flight will typically take an automobile, taxi, bus, or train to the airport and then enter the terminal. Within the terminal, passengers purchase tickets, transfer their luggage, and go through security. The buildings that provide access to the airplanes (via gates) are typically called concourses. However, the terms "terminal" and "concourse" are sometimes used interchangeably, depending on the configuration of the airport.
Smaller airports have one terminal while larger airports have several terminals and/or concourses. At small airports, the single terminal building typically serves all of the functions of a terminal and a concourse.
Some larger airports have one terminal that is connected to multiple concourses via walkways, skybridges, or underground tunnels (such as Denver International Airport). Some larger airports have more than one terminal, each with one or more concourses (such as New York's La Guardia Airport. Still other larger airports have multiple terminals each of which incorporate the functions of a concourse (such as Dallas/Fort Worth International Airport).