The Australian Cattle Dog (ACD), or simply Cattle Dog, is a breed of herding dog originally developed in Australia for droving cattle over long distances across rough terrain. This breed is a medium-sized, short-coated dog that occurs in two main colour forms. It has either brown or black hair distributed fairly evenly through a white coat, which gives the appearance of a 'red' or 'blue' dog. The mask consists of a black patch over one or both eyes (for the blue coat colour) or a red patch over one or both eyes (for the red coat colour). Depending on whether one or both eyes have a patch, these are called, respectively, 'single' (or 'half') mask and 'double' (or 'full') mask. Dogs without a mask are called plain-faced. Any of these are acceptable according to the breed standard. In conformation shows, even markings are preferred over uneven markings.