A ruminant is an animal with a special kind of stomach that lets it eat grass and other tough plants that most animals can't digest. Cows, sheep, goats, deer, and giraffes are all ruminants.

Here's what makes them special: ruminants swallow their food quickly without chewing it much, then later bring it back up to chew it again. You've probably seen a cow lying in a field, calmly chewing with nothing in front of it. That cow is chewing its cud, which is partially digested food it swallowed earlier and brought back up. This process is called ruminating.

A ruminant's stomach has four main chambers that work together like a food-processing factory. The first chamber, called the rumen, is full of helpful bacteria that break down tough plant fibers. After the food ferments there, the animal brings it back up, chews it thoroughly, swallows it again, and sends it through the other stomach chambers for final digestion.

This system lets ruminants survive on grass and leaves that would give humans terrible stomachaches.

As an adjective, ruminant describes animals of this type, as in: “The cow is a ruminant.”