What is the difference between a chin-up and a pull-up?

The hand grip and muscles used is what differentiates these two exercises.

A chin-up is performed with your palms facing TOWARDSyou. This mostly works your Bicep muscles.

A pull-up is performed with your palms facing AWAY from you. This mostly works your shoulder and upper back muscles.

So on the whole, Pull-ups are harder to do than chin-ups