Basic meaning of html
XHTML stands for EXtensible HyperText Markup Language
XHTML is almost identical to HTML 4.01
XHTML is a stricter and cleaner version of HTML 4.01
XHTML is HTML defined as an XML application
XHTML is supported by all major browsers.
Why XHTML ?
Many pages on the internet contain "bad" HTML.
The following HTML code will work fine if you view it in a browser (even if it does NOT follow the HTML rules):
<title>This is bad HTML</title>
<p>This is a paragraph
XML is a markup language where documents must be marked up correctly and "well-formed".
XHTML has a more strict syntax rules in comparison of HTML. XHTML gives you a more consistent, well structured format so that your webpages can be easily parsed and processed by present and future web browsers. It also makes your website more easy to maintain, edit, convert and format in the long run.
Since XHTML is an official standard of the World Wide Web Consortium (W3C), your website will more likely will be more compatible to more browsers and will be rendered more accurately. XHTML combines strength of HTML and XML and XHTML pages can be rendered by all XML enabled devices.
XHTML defines a quality standard for your webpages, if you follows that then your web pages will be counted quality web pages and W3C certifies those pages with their quality stamp.
Web developers and web browser designers are constantly discovering new ways to express their ideas through new markup languages. In XML, it is relatively easy to introduce new elements or additional element attributes. The XHTML family is designed to accommodate these extensions through XHTML modules and techniques for developing new XHTML-conforming modules. These modules will permit the combination of existing and new feature sets when developing content and when designing new user agents.