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HTML5 is the next major revision of HTML.

HTML5 provides a number of new elements and attributes that reflect typical usage on modern Web sites. Some of them are semantic replacements for common uses of generic block and inline elements, for example nav (website navigation block) and footer. Other elements provide new functionality through a standardized interface, such as the audio and video elements.
Some deprecated elements from HTML 4.01 have been dropped, including purely presentational elements such as font and center, whose effects are achieved using CSS. There is also a renewed emphasis on the importance of DOM scripting in Web behavior.

The following is a cursory list of differences and some specific examples.