The chin-up is a strength training

Weight training

Weight training is a common type of strength training for developing the strength and size of skeletal muscles. It uses the weight force of gravity to oppose the force generated by muscle through concentric or eccentric contraction...

 exercise. The verb chinning means to do them. People frequently do this exercise with the intention of strengthening muscles such as the latissimus dorsi and biceps

Biceps

Biceps may refer to:*Biceps brachii muscle, a muscle located on the inside of the upper arm*Biceps femoris muscle, one of the hamstring muscles of the back of each thigh*Biceps , a point in a metrical pattern...

, which extend the shoulder and flex the elbow, respectively.

It is a form of pull-up

Pull-up (exercise)

A pull-up is an upper body compound pulling exercise where the body is suspended by the arms, gripping something, and pulled up with muscular effort...

 in which the range of motion is established in relation to a person's chin.
A chin up is named by bringing the chin up through space, specifically in relation to its position with the bar or other hand grips.