Syntactic agreement refers to the grammatical rule that ensures different parts of a sentence match in number, gender, or person. For example, in English, a singular subject like the cat requires a singular verb, as in "The cat runs." If the subject is plural, such as the cats, the verb must also be plural, resulting in "The cats run." This concept is crucial in many languages, including Spanish and French, where adjectives must agree with the nouns they describe in both gender and number. Proper syntactic agreement helps maintain clarity and coherence in communication, making sentences easier to understand.