What Are Socks?

No, horses generally don't wear socks under their shoes.

Socks are white markings that start at the hoof and extend to some point between the fetlock and the knee or hock.

A horse might have socks on one leg all the way to all four. Note that in some equestrian disciplines, horses with a sock on only one side are frowned upon because it can make their gait look uneven.

The chestnut horse in the center has a sock on his right hind leg. And is hamming it for the camera. Or asking me to take all that gear off his back, not sure which.