HTML i.e. Hypertext Markup Language provides a simple tag-based syntax for creating forms, embedding pictures and links, and producing other structural and presentational aspects of a web page.
XHTML (Extensible Hypertext Markup Language) is almost identical HTML with the exception of a stricter set of syntactic rules based on the XML standard. For instance, in HTML you can use an opening tag in many instances without a matching closing tag. In XHTML each opening tag must have a matching closing tag.
DHTML (Dynamic HTML) is a collection of technologies used to move beyond the static presentation of information to create more interactive web pages. Technologies that play a role in DHTML include HTML, JavaScript, Cascading Style Sheets (CSS), and the Document Object Model (DOM). CSS is used to control the presentation of the structured content defined by HTML. The DOM is a client-side programmable interface to the state of the HTML document being rendered and its associated CSS presentation. The Dynamic part of DHTML comes into play when JavaScript is used to manipulate the state of the DOM to cause the appearance or behavior of the rendered web page to change.
Credit: https://www.qualitylogic.com/Contents/Web-Testing/Technology/HTML-XHTML-DHTML.aspx
