Here's why:
* Relative because they relate the adjective clause back to the noun or pronoun they modify.
* Pronoun because they take the place of a noun or noun phrase.
Common relative pronouns include:
* who (for people)
* whom (for people, used as the object of a verb or preposition)
* whose (for possession)
* which (for things)
* that (for people or things)
Example:
* "The woman who lives next door is a doctor."
* "Who" relates back to "woman" and introduces the adjective clause "who lives next door."
Let me know if you would like more examples or have any other questions!