Deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, the fallow deer, and the chital; and the Capreolinae, including the reindeer (caribou), the roe deer, the mule deer, and the moose. Female reindeer, and male deer of all species except the Chinese water deer, grow and shed new antlers each year.
Deer live in a variety of biomes, ranging from tundra to the tropical rain-forest. While often associated with forests, many deer are ecotone species that live in transitional areas between forests and thickets (for cover) and prairie and savanna (open space).