Dynamic HTML is used to designate a technique of creating interactive web sites by using a combination of the static markup language HTML, the browser programming language Javascript and the style definition language Cascading Style Sheets. Besides Flash it is the most often used technique for animating web pages.
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.
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)