A common noun is a general name for a person, place, thing, or idea. Unlike proper nouns, which name specific entities (like John or Paris), common nouns refer to general categories, such as teacher, city, or book. They do not require capitalization unless they begin a sentence. Common nouns can be singular or plural. For example, the word dog is a common noun that refers to any dog, while dogs refers to more than one. These nouns help us communicate about everyday objects and concepts without specifying a particular instance.