In linguistics, a noun phrase is a phrase whose Head is a noun.
For example, in the sentence Most young people in England have been to school, the phrase most young people in England is a noun phrase. A noun phrase can be a single word: in See Jane run, Jane could be described as a noun phrase. Single pronouns can also act as noun phrases.
In English, for some purposes noun phrases can be treated as single grammatical units. This is most noticeable in the syntax of the English genitive case. In a phrase such as The King of Sparta's wife, the possessive clitic 's is not added to the King who actually owns the wife, but instead to Sparta, to which the wife only remotely belongs. The clitic modifies the entire phrase King of Sparta.
