Subject-verb agreement is a grammatical rule that ensures the subject of a sentence matches the verb in number. This means that if the subject is singular, the verb must also be singular, and if the subject is plural, the verb must be plural. For example, in the sentence “The cat runs,” the singular subject “cat” agrees with the singular verb “runs.” In contrast, in the sentence “The cats run,” the plural subject “cats” agrees with the plural verb “run.” Proper subject-verb agreement helps maintain clarity and coherence in writing, making it easier for readers to understand the intended meaning.