A post is a particular instance of someone’s write-up. It could be a single sentence, a paragraph, or an article. It’s not called a post until it appears in a public place, like Facebook for example. A blog is a website run by one person or organization, where there is a collection of the post.

The most common type belongs to a person, and this person writes articles which they post there. (Notice post used a verb; it comes from placing posters on wooden posts.) Each article is a post. Posts are sometimes called blogs.

Writing a post or posts is called blogging. But the difference in between both of them is that you can have a blog website, where you make posts. The blog is something with a theme, such as an author’s website blog about his books.