A noun phrase is a group of words that functions as a noun. It consists of a noun or pronoun as the headword, which can be modified by adjectives, determiners, and other nouns. Noun phrases can function as subjects, objects, or complements in a sentence.
For example, in the sentence "The big red house on the hill is for sale," the noun phrase "the big red house on the hill" functions as the subject of the sentence. The headword is "house," which is modified by the adjectives "big" and "red" and the prepositional phrase "on the hill."