The lateral deltoid is one of the three muscles that make up the deltoid muscle group in the shoulder. It is located on the outer part of the shoulder and is primarily responsible for arm abduction, which is the movement of raising the arm away from the body. This muscle plays a crucial role in various activities, such as lifting and reaching. In addition to its function in arm movement, the lateral deltoid contributes to the overall shape and appearance of the shoulder. Strengthening this muscle can enhance shoulder stability and improve athletic performance in sports that require overhead movements, such as swimming and tennis.