An article (a/an/the) before a noun is a determiner. So is a number, a possessive (my/his), some kinds of pronouns (this/those) and a few other kinds of word (which).
Countable nouns need a determiner before the noun, but it doesn't have to be an article.
- The boys talked.
- My boys talked.
- Which boys talked?
- Five boys talked.
- Several boys talked.
- Those boys talked.
No. Descriptive adjectives are adjectives like "red". Numbers before a noun are called "limiting adjectives." Rather than describe the noun, they restrict the noun. Words like "the," "a," and "other" are also classified as limiting adjectives.