tundra

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

• noun A treeless area beyond the timberline in high-latitude regions, having a permanently frozen subsoil and supporting low-growing vegetation such as lichens, mosses, and shrubs.
• noun A similar area found at high elevations.

from The Century Dictionary.

• noun In the northern part of Russia (both in Europe and in Asia), one of the nearly level treeless areas which occupy most of that region, and do not differ essentially from the steppes, except that, lying further north, their climate and vegetation are more decidedly arctic than those of the country to the south, with a corresponding increase in the number of small lakes and morasses.
• noun A marshy moss-covered plain or rolling district, deeply frozen in winter and thawed at the surface in the summer. Such plains occupy large areas of arctic Asia and North America.

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

• noun One of the level or undulating treeless plains characteristic of northern arctic regions in both hemispheres; the term is most commony associated with the arctic plains of Siberia. The tundras mark the limit of arborescent vegetation; they consist of black mucky soil with a permanently frozen subsoil, but support a dense growth of mosses and lichens, and dwarf herbs and shrubs, often showy-flowered.

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

• noun A flat and treeless arctic biome.

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

• noun a vast treeless plain in the Arctic regions where the subsoil is permanently frozen