Resin is a thick, sticky substance. Trees like pine make natural resin, a sap that oozes out and slowly hardens - this is the same stuff that, over millions of years, can turn into amber. There's also man-made resin, used to make plastics, glue, and paint, and a special kind of resin is rubbed on violin bows so they can grip the strings and make sound. So the word covers both something a tree makes and something a factory makes, as long as it's this thick, sticky, hardening kind of substance.