Ring compounds with delocalized electrons originally were called aromatic molecules because many of them have a pronounced odour.

The term long since has been stretched beyond its original meaning, and now includes all ring molecules similar to benzene that have delocalized electrons and low chemical reactivity.

Nonaromatic hydrocarbons are called aliphatic hydrocarbons, a term that originally meant "fatty."

The primary chemical reactions of aromatic molecules are substitutions at the edges of the rings, and not addition across double bonds.