Resin, REHZ uhn, is any one of a class of natural substances used in varnishes, medicines, soaps, paints, and other applications. Natural resins have largely been replaced by synthetic resins. Natural resins may be divided into three main groups: (1) those that flow from plants as the result of wounds; (2) those extracted from wood by solvents; and (3) fossil resins found with the preserved remains of animals and plants. A scale insect of the acacia tree also produces a resin, called lac.