snow line

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. The limit of continual snow, or the line above which a mountain is continually covered with snow. The snow-line is due primarily to the decrease of the temperature of the atmosphere with increase of altitude. In general, the height of the snow-line diminishes as we proceed from the equator toward the poles; but there are many exceptions, since the position of the snow-line depends not only upon the mean temperature, but upon the extreme heat of summer, the total annual snowfall, the prevalent winds, the topography, etc. For these reasons, the snow-line is not only at different heights in the same latitude, but its position is subject to oscillation from year to year in the same locality. Long secular oscillations in the height of the snow-line are evidence of corresponding oscillations of climate. In the Alps the snow-line is at an altitude of 8,000 to 9,000 feet; in the Andes, at the equator, it is nearly 16,000 feet.

Wiktionary

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

GNU Webster's 1913

1. n. lowest limit of perpetual snow. In the Alps this is at an altitude of 9,000 feet, in the Andes, at the equator, 16,000 feet.

WordNet 3.0

1. n. the line on a mountain above which there is perpetual snow and ice