The combined use of HTML/XHTML and JavaScript (usually along with the DOM and Cascading Style Sheets) to create a dynamic = interactive Web pages.

Drop down menus and roll-over links are the most common forms of DHTML found on web sites today. Technologies such as AJAX and/or JASON take this to the next level combining DHTML with XML and data transfer to create web pages (typically parts of web applications) that can be updated without refreshing the entire page.