Object pronouns are words that replace nouns in a sentence to avoid repetition. They refer to the person or thing receiving the action of the verb. Common object pronouns include me, you, him, her, it, us, and them. For example, in the sentence "I see John," the object pronoun can replace John to become "I see him." These pronouns are typically used after verbs or prepositions. For instance, in the sentence "She gave the book to me," the object pronoun me indicates who received the book. Using object pronouns helps make sentences clearer and more concise.