HTML 5 is the upgraded version of HTML 4 come up with many features. The objective of introducing HTML 5 to enrich the hyper text language by incorporating new tags which reduces the usage of scripting and flash object.
Currently every browser not support the HTML 5 but the big name including Chrome,Firefox, IE and Opera has been working to add the support of HTML 5. You can test your browser compatibility in http://www.html5test.com, it scores your browser out of 400 score. More score means more features of HTML 5 is supported by the browser.
So far the Google chrome browser is the winner with the highest score of 314 pint out of 450 which means it supports 70% features of HTML 5.