snow line

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

• noun The lower altitudinal boundary of a snow-covered area, especially of one that is perennially covered, such as the snowcap of a mountain.
• noun The fluctuating latitudinal boundaries around the polar regions marking the extent of snow cover.

from The Century Dictionary.

• noun The limit of continual snow, or the line above which a mountain is continually covered with snow.

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

• noun The altitude, in a mountainous region, above which the ground is covered with snow, at any particular time.

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

• noun the line on a mountain above which there is perpetual snow and ice