The airside is the part of an airport
where people go to board planes—in contrast to the landside
, where they may be doing other things. Once you show your boarding pass
to the security
personnel at Checkpoint Charlie
, you're in the airside.
The airside of an airport can follow many designs. Gatwick Airport and Miami International Airport have ridiculously long piers with moving walkways to help passengers get from one end to the other. At Dallas Fort Worth International Airport, the airside is on the outer edge of semicircular terminals, and thus only a few hundred feet away from the parking lot. Go to Pittsburgh International Airport, and the airside is in a separate building altogether.