The Bootlid Tailgate is the lifting cover for the boot space on a saloon vehicle or the lifting door on a hatchback or estate vehicle. In the latter it will include the rear window, in the former it will be a solid piece of bodywork.
The Bootlid is attached by hinges to the boot space/luggage compartment at the rear of the vehicle.The hinged Bootlid Tailgate, with the window, lifts, opening the rear end of the passenger compartment. The Bootlid Tailgate will house a heated screen with a wiper/wash system and possibly lighting.
The usual reason for replacement is collision damage.