1. A noun: When you're talking about a piece of writing, like an article in a newspaper or magazine.
2. A part of speech: This is the most common usage. Articles are words like "a," "an," and "the" that come before nouns to specify whether the noun is singular or plural, definite or indefinite.
So, the answer to your question depends on how you're using the word "article." If you're talking about a type of word, it's a part of speech. If you're talking about a piece of writing, it's a noun.