For example, in the sentence Most young people in England have been to school, 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.
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 Queen of England's knickers, the possessive clitic 's is not added to the Queen who actually wears the knickers, but instead to England, to which the knickers only remotely belong. The clitic modifies the entire phrase Queen of England.