Deer or true deer are hoofed ruminant mammals forming the  Cervidae.

The Cervinae, which includes the muntjac, elk (wapiti), red deer, and fallow deer, and the Capreolinae, which includes the reindeer (caribou), white-tailed deer, roe deer, and moose.

Every year, male deer of the vast majority and female reindeer develop and shed new antlers.

They are distinct from permanently horned antelope, which belong to a separate (Bovidae) within the same order of even-toed ungulates (Artiodactyla).