The chin-up (also known as a chin or chinup) is a strength training exercise. People frequently do this exercise with the intention of strengthening muscles such as the latissimus dorsi and biceps, which extend the shoulder and flex the elbow, respectively.
It is a form of pull-up in which the range of motion is established in relation to a person’s chin.
In the 1970s and 1980s, the term chin-up not only included an overhand/pronated (“palms away”) grip, but some authors used it as the default meaning of the term, with an underhand/supinated (“palms toward”) grip called a “reverse” grip. Even in the 2010s “chin-up” still includes palms-away lifting. The term “chin-up” is still regularly used refer to pulling using an overhand-grip.
Both pull-ups and chin-ups are two of the best exercises for back and overall upper body conditioning. However, they target the muscles a bit differently. Both exercises will work the latissimus dorsi and biceps, but standard chin-ups—with an underhand grip—place more emphasis on the biceps.
Source of the text: Wikipedia