blowhole

(marine biology) The spiracle, on the top of the head, through which cetaceans breathe.

(geology) 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.

(geology) A vent for the escape of steam or other gas.

(metallurgy) An unintended cavity filled with air in a casting product.

(computer hardware) A vertical opening in the top of a computer case that lets hot air (primarily from the CPU heat sink) escape quickly.