What is a relating clause?

a clause introduced by a relative pronoun; "who visits frequently' is a relative clause in the sentence John, who visits frequently, is ill'"

A relative clause is a subordinate clause that modifies a noun. For example, the noun phrase the man who wasn't there contains the noun man, which is modified by the relative clause who wasn't there

a clause which qualifies or restricts the meaning of the noun in a noun phrase. It may be introduced by Words such as who, which and that in