is relative pronoun
A relative pronoun is used to connect a clause or phrase to a noun or pronoun. You see them used everyday with the most common relative pronouns being: who, whom, which, whoever, whomever, whichever, and that. A relative pronoun is usually seen in a sentence at the beginning of an adjective clause. An adjective clause functions as an adjective, modifying nouns and pronouns. An adjective clause starts with either a relative adverb: where, when, and why.