A polymer is a large molecule made up of smaller, repeating units, which are called monomers. They connect in long chains as well as other complicated shapes. It can be linear, “made up of one molecule after another, hooked together in a long chain. This chain is called the backbone.” (Reference) Or it can be branched, with ends coming from the backbone, like branches would come from a tree trunk. They are also called macromolecules or “large molecules”.