air hole

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A hole or opening that allows for the passage of air, especially to facilitate breathing.

from the GNU version of the Collaborative International Dictionary of English.

• A hole to admit or discharge air; specifically, a spot in the ice not frozen over.
• (Founding) A fault in a casting, produced by a bubble of air; a blowhole.
• (Aëronautics) A local region in the atmosphere having a downward movement and offering less than normal support for the sustaining surfaces of a flying machine, causing an airplane to drop suddenly. Same as air pocket.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a hole in any surface that allows air or other gases to pass, especially an opening in the surface of a frozen lake etc
• noun an air pocket
• noun the blowhole of a whale

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a local region of low pressure or descending air that causes a plane to lose height suddenly
• noun a hole that allows the passage of air