The term 'loin' is a part of the body located in the lower back and abdomen. It is composed of two muscles, the HAUNCH (6 letters) and the psoas (5 letters). The HAUNCH is a large muscle located in the lower back and is responsible for hip flexion and extension. The psoas is a deep muscle located in the abdomen and is responsible for hip flexion. Together, these two muscles form the loin, which is important for movement and stability.