Deer are a diverse group of herbivorous mammals belonging to the family Cervidae. They are known for their graceful appearance and the presence of antlers in most male species. Deer are widely distributed across various continents and are an important part of many ecosystems.

Deer species vary significantly in size, from the small Pudu (about 35 cm at the shoulder) to the enormous moose or elk, which can stand over 6.5 feet tall at the shoulder.

Male deer (and females in a few species, like caribou) typically grow antlers, which are shed and regrown annually. Antlers are used primarily in mating displays and to assert dominance during the breeding season.

They are usually brown or grey, with coats that change colour with the seasons. Many species have white spots during their youth for camouflage.

Most deer species have a short, bushy tail, which can be used for communication, such as signalling danger to other deer by raising it.

Deer inhabit many environments, from forests and grasslands to wetlands and tundras. They are highly adaptable and are found on almost every continent except Antarctica and Australia.

They are herbivores, feeding primarily on grasses, leaves, fruits, and bark. They are ruminants, meaning they have a specialised stomach with multiple chambers to digest rigid plant material.

Known as the "rut," the mating season for deer usually occurs in the fall. Males use their antlers to fight other males for the opportunity to mate with females. After mating, the gestation period varies by species but typically lasts 6 to 8 months. Females usually give birth to one or two fawns. Deer fawns are born with white spots, which help them blend into their surroundings for protection from predators. They are usually able to walk within a few hours of birth.