An underhand grip, also known as a supinated grip, is a hand position where the palms face upward or toward the body. This grip is commonly used in various exercises, such as pull-ups and bicep curls, to target specific muscle groups more effectively. In strength training, using an underhand grip can engage the biceps and latissimus dorsi muscles more than an overhand grip. It is important to maintain proper form while using this grip to prevent injury and maximize the benefits of the workout.