From the book’s description:
The obi is a sash worn with various styles of Japanese clothing to secure it in place and to enhance the shape of the body. Obie are worn with kimono by both men and women and are traditionally made of silk, often in colorful, decorative designs.
The Obi Yoga socks feature a pattern that integrates the ribbing and the body and uses the pkok maneuver, alternated with garter stitch, to create obilike bands in the design. These unusual socks have no heel or toe, but rather a stirrup that slides under the instep of the foot. This construction makes them particularly useful during yoga classes, where the exposed foot allows for better traction on the floor or mat. They’re also perfect when you are getting a pedicure or when you simply want to wear socks with flip-flops for any reason.