The latissimus dorsi , also known simply as latissimus, is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline.

The word latissimus dorsi (plural: latissimi dorsi) comes from Latin and means "broadest [muscle] of the back", from "latissimus" and "dorsum" . The pair of muscles are commonly known as "lats", especially among bodybuilders.