The deltoid muscle, also known as the shoulder muscle, is responsible for the movement and stability of the arm and shoulder. Other terms often used to refer to the deltoid muscle include the triangular muscle and the shoulder blade muscle. It is located on the outer part of the shoulder and is commonly used in exercises such as shoulder raises and lateral raises. In addition to these synonyms, some may refer to the deltoid muscle as the delt, or even use the term "shoulder cap" to describe the bulging shape of the muscle on some individuals. Regardless of the term used, the deltoid muscle is a crucial part of upper body strength and mobility.