A noun is a person, place, or thing. There are probably as many different definitions of a noun as there are grammar teachers, some including more specific items like ideas, events, eras, and so on. However, to keep things as simple and easy to remember as possible, it’s fine to let the extremely vague term “thing” do its job of being as unspecific as possible to cover any other terms that could be included. Nouns serve three basic purposes. They may function as a subject of a clause, an object of a verb, or a predicate nominative.