Noun
A hole to admit or discharge air; specifically, a spot in the ice not frozen over.
A fault in a casting, produced by a bubble of air; a blowhole.
Source: Webster's dictionaryJust stick the Ravi in the neck of the bottle and place your thumb over their air hole to control the flow, then pour—slower for cooler, faster for warmer. Source: Internet
Cut a little cross into the centre of the pie - you must make an air hole or the build up of steam inside the pastry case will cause the pie to explode along the edges. Source: Internet