Once you have mastered the basics of HTML, there is still much to learn. You might be asking yourself "whats after HTML"? Advanced HTML would be your next step. Keep up with the times on HTML, it changes just like everything else!
DHTML is "Dynamic Hypertext Markup Language". It is fancy html. DHTML allows full control of the html document. No longer are pages limited to being defined while the page is being loaded. After displaying the page, any portion of the page can be dynamically and immediately changed. For example, an application can contain an outline that the user expands and collapses with the results displayed instantaneously.
VRML stands for "Virtual Reality Modeling Language". It is used to author virtual reality worlds for use on the internet. VRML is a scene description language, not a programming language. This is the developing 3D modeling language for use on the internet.
XML stands for "Extensible Markup Language". It is a meta- language. It is useful to SGML developers wanting access to the Web and Web developers who are fixed to HTML. Document developers working in XML can create their own element-sets, specific to their own documents, and use the Web as an avenue of distribution. XML gives new life to the Web by being the best of SGML and HTML.
XSL stands for "Extensible Stylesheet Language", and is a member of the XML family. It uses style sheets to display simply structured XML documents.
SGML stands for "Standard Generalized Markup Language". It is based on HTML and XML. SGML ignores page or screen layout and concentrates solely on the structure.
PERL stands for "Practical Extraction and Report Language". It is an interpreted language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical rather than beautiful.
ASP stands for "Active Server Pages". ASP allows you to design web pages that can make displaying, manipulating and editing databases quick and easy.
PHP stands for "PHP: Hypertext Preprocessor" is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
CSS stands for "Cascading Style Sheets is a simple mechanism for adding style (e.g. fonts, colors, spacing) to Web documents.
It is suggested of course that you know HTML backwards and forwards before attempting to learn something different and wondering whats after HTML. Knowing HTML will give you a good foundation when you are ready to learn something different.