What type of pronoun relates one part of a sentence to a noun or pronoun in another part of the sentence?

A relative pronoun relates to a noun or a pronoun in the sentence.

The relative pronouns are: who, whom, whose, which, that.

Example sentences:

My brother, who attends the university, will be home for the holiday.

The person to whom you give the completed application is the personnel manager.

The man, whose car I hit, was very nice about it.