HTML5 is the latest version of HTML that adds new elements and attributes. It is being developed by the W3C and WHATWG to make HTML more semantic, customizable and multimedia-capable. Key features of HTML5 include less complex header code, new semantic tags like <article> and <section>, multimedia embedding with <video> and <audio> tags, canvas drawing with JavaScript, and web storage with localStorage and sessionStorage objects. HTML5 aims to provide one standard way to embed multimedia without plugins and more options for storing data on the client-side.