Baidu Encyclopedia has made it very clear:

An application HTML standard under the Standard Universal Markup Language. Since HTML4.01 was released in December 1999, subsequent HTML5 and other standards have been shelved. In order to promote the development of the Web standardization movement, some companies have joined forces to An organization called
Web Hypertext Application Technology Working Group (Web Hypertext Application Technology Working Group
-WHATWG) was established. WHATWG focuses on Web forms and applications, while W3C (World Wide Web Consortium, World Wide Web Consortium) focuses on XHTML2.0. In 2006, the two parties decided to collaborate to create a new version of HTML.
The predecessor of the HTML5 draft was called Web Applications 1.0. It was proposed by WHATWG in 2004 and accepted by W3C in 2007, and a new
HTML working team was established. The first official draft of HTML 5 was released on January 22, 2008. HTML5
is still a work in progress. However, most modern browsers already have some HTML5 support.
On December 17, 2012, the World Wide Web Consortium (W3C) officially announced that the HTML5 specification, which has condensed the efforts of a large number of network workers, has been officially finalized. According to the W3C's speech: "HTML5 is the cornerstone of the open Web network platform."
On May 6, 2013, the official draft of HTML
5.1 was announced. The specification defines the fifth major version, the first to revise the core language of the World Wide Web: Hypertext Markup Language (HTML). In this version, new features are continuously introduced to help web application authors in an effort to improve interoperability of new elements.
Since the release of this draft on December 27, 2012, nearly a hundred modifications have been made, including HTML and XHTML tags, related APIs, Canvas, etc., as well as HTML5 image img tags and svg Improvements have also been made and performance has been further improved.

The general meaning is that HTML5 was developed by WHATWG, which is dedicated to web forms and application development, and W3C, which is focused on XHTML.

So I think html5 can be regarded as composed of two parts, one part is the html tag, and the other part is the many APIs related to JS.