A noun is a word that generally functions as the name of a specific object or set of objects, such as living creatures, places, actions, qualities, states of existence, or ideas. Nouns are everywhere in our writing and can play different roles in a sentence, such as the subject, direct object, indirect object, subject complement, object complement, appositive, or modifier. Some examples of nouns include cat, bicycle, Taylor Swift, and Kuala Lumpur.

Nouns can be classified into different types, such as proper nouns, common nouns, concrete nouns, abstract nouns, countable nouns, and uncountable nouns. Proper nouns refer to specific people, places, or things and are always capitalized, while common nouns refer to general people, places, or things and are not capitalized unless appearing at the beginning of a sentence or in a title. Concrete nouns refer to physical objects that can be perceived by the senses, while abstract nouns refer to ideas, emotions, or concepts. Countable nouns can be counted and have both singular and plural forms, while uncountable nouns cannot be counted and do not have a plural form.

In summary, a noun is a word that names a person, place, thing, or idea and can play different roles in a sentence. Nouns can be classified into different types based on their characteristics.