clearance

Clearance is the vertical, horizontal, or total spatial parameters allowed within a structure, pathway, or part of a structure for the passage of persons, vehicles, cargo, animals, etc. Any fixed protrusion into the framework to which a clearance is assigned may reduce the clearance dimensions.

The relevant space is the opening or route available for passage. A beam or another fixed projection can reduce that opening even when the surrounding structural frame is larger.

Height and width describe different limits on the same passage. A vehicle can satisfy the height limit while being too wide, so one clearance dimension does not establish all others.