Wiktionary
n. (context grammar English) A pronoun that is used as the object of a sentence, such as "me", "him" or "us" in English.
Wikipedia
In linguistics, an object pronoun is a personal pronoun that is used typically as a grammatical object: the direct or indirect object of a verb, or the object of a preposition. Object pronouns contrast with subject pronouns. Object pronouns in English take the objective case, sometimes called the oblique case or object case. For example, the English object pronoun me is found in "They see me" (direct object), "He's giving me my book" (indirect object), and "Sit with me" (object of a preposition); this contrasts with the subject pronoun in "I see them," "I am getting my book," and "I am sitting here."