Which kind of noun is harbor?

"Harbor" can be both a common noun and a proper noun, depending on how it's used:

* Common noun: When referring to a general place where ships can find shelter, "harbor" is a common noun. For example: "The ship sailed into the harbor."

* Proper noun: When referring to a specific harbor with a name, "Harbor" becomes a proper noun. For example: "The ship docked at San Diego Harbor."

So, it depends on the context!