A small animal like a squirrel which travels through the air between trees, spreading out the skin between its front and back legs to stop itself from falling too quickly.
An animal with long legs, that eats grass, leaves, etc. and can run fast. Most male deer have antlers (= horns shaped like branches). There are many types of deer.
An African or Asian animal like a deer, that runs very fast. There are many types of antelope. An antelope is a member of a number of even-toed ungulate species indigenous to various regions in Africa and Eurasia.