XHTML (Extensible Hypertext Markup Language)

XHTML stands for "Extensible Hypertext Markup Language." XHTML is based on the hypertext markup language (HTML) used for creating Web pages. It is based on the HTML 4.0 syntax, but has been modified to follow the guidelines of XML, the Extensible Markup Language. So XHTML 1.0 is sometimes referred to as HTML 5.0.

Due to "extensibility" of XHTML, custom objects and tags can be created for each Web page. To achieve this, custom tags and attributes are defined in a document type definition (DTD). XHTML has more strict syntax than regular HTML.