Conformation refers to horse's body form and size, and how horse's skeleton, muscles and fat are connected to horse's body.
Horses are born with their conformation, which does not change as the horse ages. It is possible for horses to grow and develop over time, especially if they are young or underfed, but such changes do not alter the horse's core size and shape. This innate conformation often relates to an individual horse's breed and genetic background.
Conformation is important for horse's health because horse have to carry themselves and their rider in everyday activities. A horse with poor conformation will typically need extra help from its rider in order to move correctly during various gaits and horse activities.