HTML5

It's the fifth version of HTML (Hyper Text Markup Language) presented by the World Wide Web Consortium (W3C). It unifies previous versions of the standard such as HTML 4, XHTML 1 and DOM Level 2 HTML. For the sake of complex applications it offers a new set of powerful APIs.

Some of these APIs give games applications a more flexible and stable base:

Canvas element: Allows for dynamic, scriptable rendering of 2D shapes and bitmap images. It also allow the use of webGL (allowing the gpu to take load from the cpu).

Web Audio API: A high-level API for controlling and synthesizing audio on the web.

Web storage: Adds persistent data storage to the client browser.