1 Part of a straight wall constructed between two advancing structures, such as bastions, buttresses, or piers. In a fortification it is the weakest element, and in a church it is pierced with large windows, as in a Perpendicular Gothic aisle.
2 Any plain enclosing screen-wall not supporting a roof.
3 Partition between two rooms, or subdividing a space.
4 In modern construction, a thin subordinate wall between piers or other structural members, the curtain being a filling, having no share in the support of other parts of the building. This principle was extended to the provision of entire external non-loadbearing skins, supported by the structure, and usually made of metal, glass, or some other type of cladding.
Hart, Henn, & Sontag (1985)
curtain-wall. On column-and-slab construction.