The a chin-up is a variation of the pull-up exercise in which the reps are performed with the palms facing toward the body, in an underhand position, with a grip that is narrower than shoulder-width. Like other pull-up variations, it builds strength and muscle in the upper back, biceps, and core, but it utilizes the biceps slightly more than overhand pull-ups. It can be used as a more shoulder-friendly alternative to straight-bar pull-ups, or to help perform more reps than you can perform overhand.
Strengthens the muscles of the lats (latissimus dorsi), biceps, upper back, core, and grip
Requires no equipment other than a bar
Like pull-ups, can build absolute strength for low reps, or strength endurance for higher reps
Many people find it slightly easier and shoulder-friendly than overhand pull-ups