Cows are classified as mammals. A mammal is defined as an animal that possesses a backbone, hair, mammary glands, three inner ear bones and a neocortex. Most mammals also give birth to live young, save for the egg-laying monotremes.
The most obvious unique defining characteristic of mammals is their ability to produce milk in order to feed their young. Indeed, the term mammal has its roots in the Latin word "mamma," meaning "teat." With their well documented ability to produce milk along with their hair-covered body, cows have been classified as mammals since the term was originally coined in 1758.