Definition – What does HTML5 mean?
HTML5 is a markup language that is used for structuring and presenting content on the WWW. It is a fifth and latest version of the HTML standard that was published in October 2014 by W3C in order to enhance the language with provision for the latest multimedia and also keeping it both easily readable by humans and computer. This is planned to subsume not only HTML4 but also HTML1 and DOM level 2 HTML.
Glossary Web explains HTML5
HTML5 also introduce detailed processing models in order to encourage more interoperable implementations, extends, enhance and rationalize the markup available for documents. It also introduces markup and application programming interfaces for complicated applications. HTML5 is also available to use on multiple mobile platforms because it offers features designed with low-powered devices in mind. The DOM (Document Object Model) and APIs are now fundamental parts of the HTML5 specification and it also better defines the processing for any invalid documents.