The mule deer is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer.

A deer or true deer is a hoofed ruminant ungulate of the family Cervidae. It is divided into subfamilies Cervinae and Capreolinae. Male deer of almost all species, as well as female reindeer, grow and shed new antlers each year. These antlers are bony extensions of the skull and are often used for combat between males.