A group of horses that live together permanently. In a wild or semi-wild situation, herds are usually family groups consisting of several mares, their young offspring and a stallion. Other natural herds include groups of young males (colts) or occasionally females (fillies) that have been driven away from their 'birth' herd by the dominant stallion.
In a domestic setting, a herd may be any group of horses that live together, such as a group youngsters or a group of mares and geldings of varying ages. In breeding circles, a stallion may be allowed to run with a specific group of mares, creating a breeding herd.