The phrase "left arm" refers to one of the two upper limbs on the left side of a person's body. It is anatomically known as the brachium and is part of the musculoskeletal system, consisting of bones, joints, ligaments, tendons, and muscles that work together to facilitate movement and support the body. The primary function of the left arm is to help a person perform various tasks such as lifting objects or reaching out for something, among others. Additionally, it also plays an important role in maintaining balance while standing or walking.