The spiracle, on the top of the head, through which cetaceans breathe.
A vent for the escape of gas.
A top-facing opening to a cavity in the ground very near an ocean's shore, leading to a marine cave from which wave water or bursts of air are expelled.
An unintended cavity filled with air in a casting product.
A vertical opening in the top of computer cases, that let hot air, primarily from the CPU heat sink, escape quickly.
To fill or be filled with air in an unintended cavity.