在动物学上，草食性是指主要吃植物，而不吃肉类的动物。而一些选择不吃肉类的人则被称为素食者。实际上「草食性」并非指“吃草”的动物，还包括吃木质、花粉、花蜜、水果、谷物等。在英语中，术语Graminivorous才是指“吃草的”，Graminivore是从拉丁文Graminis“草”变化而来，后半部分的vore是拉丁文的vorare（吃）。牛是典型的草食性动物，牠们并不能把肉类咀嚼及消化。许多草食动物能够消化纤维素，但并非全部，能够消化纤维素者以草叶为主食。

A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.