I've seen people talk about sites upgrading from Flash to HTML5, but there's no sign of HTML5 anywhere in their source. So what constitutes as an "HTML5 interface"? Is this term becoming the next "Web 2.0"?
You will always have people who misinterpret or misuse a term, though from what I've seen out on the web an HTML5 interface still contains HTML5 markup.
For it to become another "Web 2.0" term would mean that there wouldn't be an actual difference between HTML5 and other web languages.
This is mostly up for your own interpretation.
Agree with Christopher. Strictly it just refers to the next standard of HTML (HTML 5.0). The feeling of HTML5 becoming a buzzword is because it supports and simplifies many previously complicated/convoluted issues like embedding Flash, audio, and other media.
Here is a great primer:
I agree with previous answers (Christopher and user5514) as they state HTML5 is becoming a new buzzword and usually misenterpreted.
As a WHATWG member I feel the urge to point what HTML5 is and what isn't in short.
HTML5 is a new technology definition, intended to turn into a standard (perhaps when this happen for real, I mean, HTML5 proposal becomes a W3C recommendation, too much time passed).
Another important feature is the web related technologies interoperability (SVG, canvas, MathML, Ruby Notation...).
When analizing a new "HTML5" website, despite it contains only "old" tags, it can use a new interface on scripting part.
Ah, another point that worths to mention is: we can define new standards. On the other hand, it should worth nothing if there is no browser support - what makes the standards work in the wild.
Keep an eye into this, and have nice HTML5 experiences.