The overhead squat is a full body exercise that works the shoulders, upper back, core, hips, knees, and ankles. It involves squatting down while holding a barbell directly overhead. The document provides instructions for performing the overhead squat, including foot placement, back positioning, bar path, breathing, and common errors to watch out for. It describes the muscles worked in each phase of the movement and emphasizes keeping the knees aligned over the feet and the back in a neutral position throughout.