A herd is a social grouping of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is referred to as herding.
The term herd is generally applied to mammals, and most particularly to the grazing ungulates that classically display this behaviour. Different terms are used for similar groupings in other species; in the case of birds, for example, the word is flocking, but flock may also be used, in certain instances, for mammals, particularly sheep or goats. A group of quail is often referred to as a covey. Large groups of carnivores are usually called packs, and in nature a herd is classically subject to predation from pack hunters.