Pronoun case refers to the form a pronoun takes based on its function in a sentence. There are three main cases: subjective, objective, and possessive. The subjective case is used when the pronoun acts as the subject of a verb, such as in the sentence "I run." The objective case is used when the pronoun is the object of a verb or preposition, as in "The teacher called me." Possessive case indicates ownership, as seen in phrases like "my book" or "her car." Understanding pronoun case helps ensure clarity and correctness in communication. Proper usage enhances the effectiveness of language in conveying meaning.