An airlock is a compartment which permits passage between environments of differing atmospheric pressure or composition while minimizing the mixing of environments or change in pressure in the adjoining spaces. "Airlock" is sometimes written as air-lock or air lock, or abbreviated to just lock.

A vestibule is a small room leading into a larger space such as a lobby, entrance hall, or passage, for the purpose of waiting, withholding the larger space from view, reducing heat loss, providing storage space for outdoor clothing, etc. The term applies to structures in both modern and classical architecture since ancient times.