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 the clause to a noun, making sentences more informative and cohesive. 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. Who and whom are used for people, while which and that are typically used for things or animals. Using relative pronouns enhances clarity and detail in writing.