A relative pronoun is a word that introduces a relative clause, which provides more information about a noun. Common relative pronouns include who, whom, whose, which, and that. For example, in the sentence "The book that I read was fascinating," the word that connects the clause "I read" to the noun book. Relative pronouns help clarify relationships between different parts of a sentence. They can refer to people, animals, or things. For instance, in "The teacher who inspires me is Mr. Smith," the pronoun who links the clause to the noun teacher, giving more context about which teacher is being discussed.