Jeff Croft:

  But I think there’s actually a very good reason
  why we should, in fact, embrace the term “HTML5”
  as an overarching buzzword for this latest round
  of web standards and specifications. Our industry
  has proven on several occasions that we don’t get
  excited about new, interesting, and useful technologies
  and concepts until such a buzzword is in place.

Source: http://jeffcroft.com/blog/2010/aug/02/term-html5/ via http://www.zeldman.com/2010/08/03/html5-fuzzies/ (there is a term HART proposed in comments, I quite like that one).