A noun phrase is a group of words that functions as a noun in a sentence. It typically includes a noun and its modifiers, which can be adjectives, articles, or other descriptive words. For example, in the phrase the big red ball, "ball" is the main noun, while "the," "big," and "red" provide additional information about it. Noun phrases can vary in complexity, ranging from simple phrases like a cat to more elaborate ones like the small, fluffy cat with green eyes. They help to convey specific meanings and add detail to sentences, making communication clearer and more effective.