A piece of non-fiction prose written for a publication is one kind of article.
But a piece of a collection of something is also an article, like an article of clothing. If you're talking grammar, definite and indefinite articles are words, such as a, an, and the, whose purpose is to indicate, specify and limit a noun. An article of faith is something that is firmly believed. And an article of organization or incorporation is a section of a legal document that sets out rules for a company.