You might be forgiven for thinking DHTML is a new kind of HTML. Actually it's not really. It is just plain old HTML code. What makes it dynamic are the supporting technologies that operate on it. Without them, there is nothing dynamic about HTML at all.

Principally, it's the JavaScript and CSS style sheet support that makes HTML dynamic and it's the access to the HTML through a Document Object Model that allows us to operate on the HTML in the document.

Things are complicated a little because the dynamism can be applied at the server-end and really what we mean by DHTML is a client-end activity. Server created HTML, even though it's done with JavaScript, is not really DHTML.

Perhaps a less ambiguous description is CSS and DOM scripting. That allows some differentiation of the appearance vs. structural things you can accomplish with script driven documents.