Resins are natural or synthetic substances that are typically viscous and can harden over time. They are produced by various plants, especially trees, as a defense mechanism against injury or infection. Common examples of natural resins include amber and copal, which have been used for thousands of years in art and jewelry. Synthetic resins, on the other hand, are man-made materials used in a wide range of applications, including adhesives, coatings, and plastics. They are often derived from petroleum products and can be engineered to have specific properties, making them versatile for industries like construction and automotive.