An adjective modifies a noun or pronoun. For example, in the following sentence, pharmaceutical is an adjective that describes the noun executive.
A pharmaceutical executive donated $100,000 to the charity.
Articles are often considered to be a subcategory of the larger universe of adjectives. There are three of them: the definite article the and the indefinite articles a and an. They don’t add much in the way of detail, but they serve an important function in the English language. Like their more descriptive adjective counterparts, they modify only nouns and pronouns.
Article • Adjective • Modified Noun or Pronoun
a neon sign
a large company
the blue notebook
the first one
an exhausted, grumpy intern