ozone hole

from The American Heritage® Dictionary of the English Language, 4th Edition

• n. An area of the ozone layer, such as the large area over Antarctica or the smaller area over the North Pole, that periodically becomes depleted of ozone.

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A region of the stratosphere over Antarctica (and a smaller one over the Arctic) that is depleted of ozone in the local spring.

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

• n. an area of the ozone layer (near the poles) that is seasonally depleted of ozone