An article is a piece of writing that contains information. A blog post, on the other hand, is a shorter piece of writing that is typically published on a website.
While an article may contain more information than a blog post, the latter is typically shorter and has a more conversational tone.
While an article and a blog post may both be written in prose, the former is generally considered to be a longer form of writing while the latter is considered to be a shorter form of writing. Additionally, an article often has references and citations while a blog post does not.
Finally, an article may be published in either online or print format, while a blog post is typically only published online.