In Modern Warfare 2, one of the campaign missions - No Russian - caused quite a stir with it's controversial airport terrorist massacre. That mission took place in Zakhaev International Airport, and Terminal is based on that singleplayer mission. The map features mostly indoor combat and features some combat inside an aircraft, as well. Terminal will be coming to Modern Warfare 3 on Xbox 360 on July 17th for Elite premium members and July 18th for non-premium Elite members.
The DLC is going to be completely free of charge for both premium and non-premium members. No word yet on PlayStation 3 and PC release dates but we'll keep you informed.