To my mind at least, AJAX and DHTML are not synonymous. AJAX is one way communication with a server and updating a section of the page without refreshing the whole. While this might also be described as "dynamic html", it's not what the term DHTML was originally used to indicate. DHTML was strictly a clientside thing. Animating a page, or validation of a form, or whatever. But no matter how you look at it, it's just semantics and not terribly important.