HTML5 is the next revision of the HTML standard that introduces new semantic elements, forms improvements, and features like video playback and geolocation without plugins. It is developed through cooperation between the W3C and WHATWG and supported by modern browsers on desktop and mobile. HTML5 introduces new elements, attributes, forms improvements, local storage, websockets, and APIs for audio, video, canvas, and geolocation to build modern websites in a backwards compatible way.