It's the professional degree that veterinarians earn after completing veterinary school. It's not specific to equine medicine, as all veterinarians receive the same DVM degree.
However, some veterinarians may choose to specialize in equine medicine after graduation. This often involves completing an internship and/or residency program focusing on horses.
So, while DVM doesn't specifically mean "equine veterinarian," it is the foundation for all veterinary practice, including those specializing in horses.