A noun is all of the following EXCEPT?

A noun is a part of speech that typically refers to a person, place, thing, or idea. While "person," "place," and "thing" all describe categories of nouns, "action" does not fit this definition. "Action" is associated with verbs, which describe activities or states of being, rather than a noun, which identifies entities. Therefore, "action" is not a category of nouns, making it the correct answer to the question.