An adjective clause is a subordinate clause that modifies a noun or pronoun. It contains both a subject and verb but is not a complete thought. Relative pronouns like who, whom, whose, that, and which introduce adjective clauses and can serve as the subject or object of preposition within the clause. The relative pronoun that can often be omitted. Relative adverbs like where and when also introduce adjective clauses. Several examples are provided to demonstrate the use of relative pronouns and relative adverbs in adjective clauses.