Adjective agreement refers to the grammatical rule that requires adjectives to match the nouns they describe in gender, number, and sometimes case. In languages like Spanish and French, adjectives change their form based on whether the noun is masculine or feminine, singular or plural. For example, in Spanish, "niño" (boy) takes the adjective "alto" (tall), while "niña" (girl) takes "alta." This agreement ensures clarity and coherence in sentences. In French, the adjective "grand" (big) becomes "grande" when describing a feminine noun. Understanding adjective agreement is essential for proper sentence structure and effective communication in these languages.