A grazer is an animal, usually a herbivorous mammal, which eats grass rather than trees and shrubs. It is contrasted with browsers, which eat trees & shrubs. The life-style, dentition (teeth), and digestive system of grazers is different from browsers, to handle the problems of eating and digesting grass. This is well illustrated in the evolution of such groups as horses. Ruminants are the largest group of grazers, though many other animals also graze.
When grazers keep eating grass in an area without giving the plants time to grow back, that is called overgrazing.