article

The element for a self-contained composition that would make sense on its own — a blog post, a news story, a product card, a comment, a forum entry, a glossary term — the unit that could be syndicated, listed, or read out of context, announced as an article to assistive technology

The test is syndication: could this be lifted out and put in a feed? A post, yes; a card in a list of posts, yes (each card is one); the page’s sidebar, no. That is why the index entry component on this site is an <article> — each entry is a thing in itself — and why the content body of a glossary or resource page is one. Articles nest (comments inside a post) and carry their own <header> and <footer>, which are not landmarks. Where <section> is a part of something, <article> is a whole.