definition
strict definition
open-air structure
A building or shelter where most of the interior space is not fully enclosed.
An open-air structure is a shelter or multi-story building which is by and large not enclosed, yet is designed for human occupancy and usage.
The space is intended for people to occupy and use despite the lack of full enclosure. A shelter can provide some protection without surrounding most of its interior with walls.
Multiple levels do not make an unenclosed form a regular enclosed tall building. The degree of enclosure is separate from the number of levels.