Adjectives are words that describe or modify nouns, providing additional information about their qualities, quantities, or states. They help to convey details such as color, size, shape, and emotion, enhancing the meaning of the nouns they accompany. For example, in the phrase "a tall building," "tall" is the adjective that describes the noun "building." Adjectives can also indicate degrees of comparison, such as "taller" or "tallest."