A humpback whale using its blowhole
Kimolu and Matt explain to check Brad Boimler's "blowhole".
A blowhole was part of the anatomy of a number of cetacean species, such as whales or dolphins, comparable to the nostril.
In 1986, when James T. Kirk and Spock visited the Cetacean Institute in Sausalito, California; they observed humpback whales, one of which blew water out of its blowhole on the crowd looking over the aquarium. (Star Trek IV: The Voyage Home)
On the USS Cerritos in 2381, when Lieutenants Kimolu and Matt rescued the non-responsive Ensign Brad Boimler from drowning in Cetacean Ops, they explained that he wasn't breathing and thought that his blowhole was broken. (LD: "First First Contact")