Which of the following descriptions matches a "pastern" marking?

The description of a "pastern" marking is correctly identified as a white marking that incorporates the entire pastern joint. In equine terms, the pastern is the area of a horse's leg that lies between the fetlock and the hoof. A marking that specifically covers this joint area is characteristic of a pastern marking.

When visualizing a horse with such a marking, it would typically appear as a white band or area that encircles the pastern joint, providing a clear identifier of this specific marking type. Understanding the distinctions between different types of leg markings is crucial for recognizing and describing equine appearances accurately.

The other options describe different types of markings that correspond to various areas of a horse's leg or body, but they do not pertain to a pastern marking as defined in equine terminology. For instance, a marking that covers the entire leg would refer to a more extensive marking, while a small spot directly on the knee pertains to a different area entirely. Similarly, a marking that resembles a blanket across the back describes an entirely different marking style.