This document discusses defining and non-defining relative clauses. It defines relative clauses as clauses that provide information about which person or thing is being referred to. It discusses the relative pronouns who, whom, which, whose, and that. It explains how these pronouns are used with people and things. The document also covers using relative pronouns as subjects and objects and the position of prepositions. It introduces the relative adverbs where, when, and why. Key examples and exercises are provided.