XHTML is the latest īversionī (as it were) of HTML - which stands for Hyper Text Markup Language.
XHTML stands for eXtensible Hyper Text Markup Language. It is the code that is used for layout on the web.
For more information about the language the best place to start is the standards body responsible for the specification:
http://www.w3c.org
Throughout the XDe there are many places where you have the
option of employing XHTML. In all cases this is an option and it is not recommended that you use it unless you are proficient in itīs use and structure.