Noun-adjective agreement refers to the grammatical rule that requires adjectives to match the nouns they describe in gender, number, and 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) is masculine, so you would say "niño alto" (tall boy), while "niña" (girl) is feminine, leading to "niña alta" (tall girl). This agreement ensures clarity and coherence in communication. In English, noun-adjective agreement is simpler, as adjectives do not change form. For instance, "the big dog" and "the big dogs" use the same adjective "big" regardless of the noun's number. Understanding noun-adjective agreement is essential for mastering the grammar of languages that require it.