What is Tundra?
To put it short, tundra is a barren, usually cold, treeless and possibly windy landscape covered in only rock and tiny plants adapted to the climate. Although this desciption is similar to that of desert, tundra differs in the fact that lakes usually dot the land allowing for plenty of wildlife.
There are two types of tundra: Polar and High Altitude.
Polar tundra exists in the polar regions of the world. Usually, due to latitude, the ground is permanantly frozen. This is called permafrost.
High alititude tundra forms at high altitudes where air is colder than at the surface. Permafrost rarely exists here.
The word was derived from tunturi which means mountain which reaches above the timberline. Tundra, in Sami, means treeless land.(Thanks to GP Sobachka and Lolli for info)