Demonym

It's the name for the people from a place. I already knew the concept existed (Glaswegians are from Glasgow, Michiganders are from Michigan, outlanders are from a country besides yours, carnies are from carnivals, aggies are from Texas A&M, etc), but I didn't know that there was a name for it. Two actually: demonym is the noun version and gentilic is the adjective.

Also, geographers say demonym, if anybody ever says it. Professors of linguistics alone use the word gentilic.