The document discusses relative clauses and how they are used to provide additional information about a noun or pronoun. It defines relative pronouns and relative adverbs, and explains their function in introducing relative clauses that modify nouns and pronouns in the main clause. Examples are provided to illustrate the different relative pronouns - who, whom, whose, that, which - and how they are applied based on whether they refer to people, animals, things, or ideas. Relative adverbs - when, where, why - are also defined as connecting relative clauses about time, place or reason to the main clause.