Noun Clause
“A dependent clause that functions as a noun in a sentence is called noun clause.”
A noun clause performs same function like a noun in a sentence.
Example
What he did made a problem for his family.
In above sentence the clause “what he did” functions as a noun, hence it is a noun clause. A noun clause works as a noun that acts as a subject, object, or predicate in a sentence. A noun clause starts with words “that, what, whatever, who, whom, whoever, whomever”.
Examples
Whatever you learn will help you in future. (noun clause as a subject)
What you said made me laugh. (noun clause as a subject)
He knows that he will pass the test. (noun clause as an object)
Now I realize what he would have thought. (noun clause as an object)