A noun is a part of speech that refers to a person, place, thing, idea, or concept. Nouns can function as the subject of a sentence, the object of a verb, or the object of a preposition. They can be either common nouns (general names like 'dog' or 'city') or proper nouns (specific names like 'Fido' or 'New York').
The word 'noun' comes from the Latin word "nomen," which means 'name.' This Latin term evolved through Old French before becoming 'noun' in Middle English.