A grammatical error occurs when the rules of a language are not followed, leading to incorrect sentence structure or word usage. These errors can include mistakes in verb tense, subject-verb agreement, punctuation, and word choice. For example, saying "She go to the store" instead of "She goes to the store" is a grammatical error. Grammatical errors can affect the clarity and effectiveness of communication. They may confuse the reader or listener, making it difficult to understand the intended message. Common types of grammatical errors include run-on sentences, fragments, and misplaced modifiers. Correcting these errors helps improve writing and speaking skills.