Well, Html 5 is the updated version of HTML. It is the same as HTML much gives facility for audio and video tag. HTML 5 comes with some extra tags that HTML doesn't have. HTML5 also have JS GeoLocation API assits in recognize places.
You may be interested in this posting from the W3C which covers the differences between HTML and HTML5. Topics covered...encoding changes, doctype declaration, obsolete elements, new elements, attribute changes, etc.
HTML is a vocabulary: it defines what kinds of elements you can write (e.g. BODY, P, LI, etc.) but isn't very strict about how you write it .
HTML5 is the next-generation version of HTML (the current version of HTML 4)not a standard yet, partially supported by some browsers (not supporting ie6&ie7) . in html5 you can use the canvas to do animation and shapes and the semantic is great because you can use new tags like : <head>,<article>,<footer> etc.
If you are considering deploying a new website, you should start to use the HTML5 Doctype. This doesnt meant that you have to include new HTML5 elements that some browsers do not support yet. As newer browser versions appear, more support for HTML5 elements will be available.
HTML 5 is the advanced verision version of HTML i.e it is the 5th verision of HTML standard. Html 5 differs from HTML in its structure.
Other additional functionalities provided by HTML 5 are: