Which marking includes the fetlock joint and is commonly referred to as a sock?

The marking that includes the fetlock joint and is commonly referred to as a sock is known as the ankle. In equine terminology, the term "ankle" is often used to describe the area around the fetlock, which is the joint located above the hoof. When a horse has white hair or markings that extend from the hoof up to and around the fetlock, this is informally termed a "sock."

This terminology helps to provide a clearer understanding of where the marking is located on the horse's leg and distinguishes it from other markings that may occur higher or lower on the leg, such as those defined by the coronet or pastern. Understanding these terms is crucial for horse evaluation, as markings can play a role in breed standards and identification.