Mastic is a resin obtained from the mastic tree. It is also known as tears of Chios, being traditionally produced on the island Chios, and, like other natural resins, is produced in "tears" or droplets.

In polymer chemistry and materials science, a resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses mainly on naturally occurring resins.