What does Back Cinch mean?

Also known as martingale, the back cinch with a back buckle was used to tighten the waist on jeans before widespread use of belts; hence the term ‘buckle back’.

Heddels explains Back Cinch

Most jean makers abandoned them by 1942; with renewed interest in vintage-style looks, cinch backs have returned on modern jeans including Evisu, Atelier La Durance and Levi’s®.

Additional Resources

Examples of LVC‘s Back Cinch: