Noun Clause

A noun is used as a subject or an object.
A noun clause is used as a subject. In other words, a noun clause is used in the same ways as a noun.
A noun clause is a clause functioning as a noun. It has its own subject and verb.
A noun clause does the work of a noun in a sentence or phrase. It is a group of words containing a subject and a finite verb of its own. noun clauses usually begin with words like how, why, what, where, when, who, that, which, whose, whether, etc. Also words like whoever, whenever, whatever and wherever.

Exemple:

• I think that she is a great player.
• Who is he? I don't know who he is.