Relative Pronoun : A pronoun when connect two statements it’s called relative pronoun. We may call it conjunctive pronoun however it’s called relative pronoun as it refers or relates to some noun going before which is called Antecedent.
Look at the examples below:
I met Harry. Harry just had return.
I have found pen. I lost the bell
Here is the book. You lend me the book.
Let’s combine the above written sentences:
-I met Harry who had just returned.
-I have found pen which I lost.
-Here is the book that you lent me.
Learn more about Pronoun and Types of Pronouns here.