A noun phrase is a group of words that functions as a noun in a sentence. It typically includes a main noun, known as the head, along with modifiers that provide additional information. For example, in the phrase the big red ball, "ball" is the head noun, while "the," "big," and "red" are modifiers that describe it. Noun phrases can vary in complexity, ranging from a simple noun like cats to more elaborate phrases like the friendly neighbor's playful dog. They can serve various roles in a sentence, such as the subject, object, or complement, helping to convey clear and detailed meaning.