What is the scientific definition of tundra?

Susan Steiner

Great question and what a place to begin!This may or may not be the best scientific explanation, which I retrieved from a free online dictionary:
A treeless area between the icecap and the tree line of Arctic regions, having a permanently frozen subsoil and supporting low-growing vegetation such as lichens, mosses, and stunted shrubs.
My ideas about it so far is that it can be tussocky and wet!
http://www.thefreedictionary.com/tundra