Relative pronouns are words that introduce relative clauses, which provide additional information about a noun. Common relative pronouns include who, whom, whose, which, and that. They help connect ideas in a sentence, making it clearer and more informative. For example, in the sentence "The book that I read was fascinating," the word that links the clause to the noun book. These pronouns can refer to people, animals, or things. When referring to people, who and whom are often used, while which and that are typically used for objects or animals. Using relative pronouns enhances sentence structure and coherence.