Dynamic HTML or DHTML designates a technique of creating interactive web sites by using a combination of the static markup language HTML, a client-side scripting language (such as JavaScript) and the style definition language Cascading Style Sheets.
It may be used to create small applications in the browser: for example to ease navigation, to create interactive forms or to create interactive exercises to use in e-learning. Besides Macromedia Flash it is the most often used technique for animating web pages.
To the dismay of some web developers, Dynamic HTML appears difficult to develop and debug, as the different web browsers have varying degrees of support to the aforementioned technologies, and the huge range of screen sizes commonly used by clients means the end look can be fine-tuned only on for a limited number of browser/screen size combinations. However recent browsers (version number 5.0 and up) share a common Document Object Model which facilitates the use of this technology considerably if one just writes web pages for these browsers.
Web-Reference: http://www.xs4all.nl/~ppk/js/index.html (comprehensive site with test examples and instructions on how to write DHTML code which runs on several browsers)