In HTML4, documents were organized by sections (`<div>` elements) with sub-sections (`<h1>`, `<h2>`, `<h3>`, etc.). With HTML5, released in October 2014, new element tags allow documents to be organized based on content.
Semantic HTML elements provide meaning to browsers, developers, and users of a site. In contrast to elements like `<div>` or `<span>`, which convey no information about their contents, semantic elements like `<header>` and `<footer>` more clearly indicate the purpose of each section of a website. Heading tags should still be used along with semantic tags.
*`<header>` defines a header for the document or a section
*`<footer>` defines a footer for the document or a section
*`<nav>` defines navigation links in the document
*`<main>` defines the main content of a document
*`<section>` defines a section in the document—the spec defines this as “a thematic grouping of content, typically with a heading," so you can think of it as being like a chapter
*`<article>` defines an article in the document
*`<aside>` defines content aside from the page content
*`<address>` defines the contact information for the author/owner of a document or an article
*`<figure>` defines self-contained content, like illustrations, diagrams, photos, code blocks, etc. <sup>2</sup>
*`<bdi>` defines a section of text that might be formatted in a different direction from other text (for instance, a quote in Hebrew or Arabic in an otherwise-English article)
1. [Lee, Michelle. "An Overview of HTML5 Semantics." *CodePen*. February 16, 2016. Accessed: October 24, 2017](https://codepen.io/mi-lee/post/an-overview-of-html5-semantics)
2. [Bidaux, Vincent. "HTML5 semantic elements and Webflow: the essential guide." *Webflow*. December 16, 2016. Accessed: October 24, 2017](https://webflow.com/blog/html5-semantic-elements-and-webflow-the-essential-guide)
Refer to the [MDN Web Docs article](https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Using_HTML_sections_and_outlines) about HTML sections and outlines.
For some history, this 2001 [article in Scientific American](https://www-sop.inria.fr/acacia/cours/essi2006/Scientific%20American_%20Feature%20Article_%20The%20Semantic%20Web_%20May%202001.pdf) about the semantic web was co-authored by Tim Berners-Lee, the inventor of the World Wide Web.