Gum is a sticky substance that oozes out of a tree or another plant, and chewing gum is the stuff you blow bubbles with or stick under your desk. Yuck.
Natural gum has many uses, including as a thickener in food products. Chewing gum, however, has only one real use: it's made to be chewed but not swallowed. This kind of gum often has a fruity or minty flavor, and can sometimes be blown into bubbles. When you gum something up, you clog or block it — or you make it sticky. Completely different gums are the soft flesh inside your mouth where your teeth are rooted.