A ruminant is any hooved animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud, then eating the cud. Ruminants include cows, goats, sheep, camels, llamas, giraffes, bison, buffalos, deer, wildebeest, and antelope. The suborder Ruminantia includes all those except the camels and llamas, which are Tylopoda. Ruminants also share another anatomical feature in that they all have an even number of toes.

Ruminants have a stomach with four chambers which are the rumen, reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with bile to form the cud (or bolus). Especially, cellulose is broken down into glucose in these chambers using symbiotic bacteria. The cud is then regurgitated, chewed slowly to completely mix it with the bile, and it further breaks down fibers. The re-swallowed cud then passes through the rumen into the next stomach chambers, the omasum, where water is removed. Then, the cud is moved to the last chamber, the abomasum. The digested food in the abomasum is finally sent to the small intestine, where the absorption of the nutrients occurs.

It is interesting to note that almost all glucose produced by the breaking down of cellulose is used by the symbiotic bacteria. Ruminants take their energy in the volatile fatty acids produced by these bacteria: acetic acid, propionic acid and butyric acid.

One of the requirements of kashrut for a land animal is the animal chewing its cud.