In grammar terms, an adjective is a word that modifies a noun or pronoun. You might have learned that it’s a 'describing word' back in elementary school.
Adjectives tell the reader what sort, how many, what size or whose. Adjectives can also be used to add more detail to a noun. [excerpt]
Tenielle Fordyce-Ruff, Back to Basics, Part V: Adjectives, 58(9) Advocate 44 (2015).