Equi-stretch by Equestrian" refers to riding pants designed for horseback riding, emphasizing flexibility and comfort due to the stretchy fabric blend. Equi-stretch: This term indicates the pants are made with a stretchable fabric, a common feature in modern riding pants for comfort and mobility. Equestrian: This signifies the pants are designed for horseback riding, providing the necessary protection and flexibility for the rider. Size S28. This is from Kentucky 1973, I was taking English riding and jumping lessons. I was only a few months in when my husband was transferred to Colorado so these are lightly used.