What characteristic defines a noun?

A noun is fundamentally defined as a word that identifies a person, place, or thing. This characteristic is essential because it allows nouns to serve as the basic building blocks of sentences, functioning as the subjects or objects in various constructions. For instance, in the sentence "The dog runs," the word "dog" is a noun that specifies a living being. Similarly, nouns can refer to places, like "city," or objects, such as "book." This identification role is crucial in both everyday language and more complex literary structures, allowing for clear communication of ideas and concepts. This means that a noun encapsulates entities that we can think about, refer to, and discuss, making it a foundational element of language.