A sealed, airtight chamber, such as in a manned spacecraft or submarine, used to provide access to and from the sealed area without allowing air out or water in.
A vestibule, foyer or entranceway with doors to the exterior on one end and doors to the interior on the other, functioning to keep indoor and outdoor air, humidity, and air temperatures separate.
Something that forms an obstacle to continued activity; a blockage or obstruction.
A pause or halt of some activity.