Given a choice between a sirloin steak and a pile of grass, an herbivore will take the grass every time. If grass isn't on the menu, a salad will do. Herbivores eat plants.
The herb in herbivore reminds you that herbivores eat plants rather than other animals. If you know any giraffes, deer, or vegetarians, you might have some herbivore friends. If you have a friend named Herb, let him know he's safe around them. Unless Herb is your favorite houseplant.