A ruminant is an ungulate that eats and digests plant-based food such as grass.
Ruminating mammals include cattle, goats, sheep, giraffes, bison, yaks, water buffalo, deer, camels, alpacas, llamas, wildebeest, antelope, pronghorn, and nilgai. All of them are Artiodactyla, cloven-hoofed animals.
The word "ruminant" comes from the Latin word ruminare which means "to chew over again". They have a more complex digestive system than other vegetarians. Digestion of food is always done mainly by microorganisms, and in ruminants it is digested twice.