What is the difference between XHTML and HTML?

Extensible Hypertext Markup Language (XHTML), a hypertext and markup programming language derived from HTML, is used to create web pages. Hypertext Markup Language (HTML) is a hypertext and markup programming language. Lists, tags, and attributes in HTML can be written in either uppercase or lowercase because case is not sensitive to HTML, whereas case may be sensitive to XHTML.

While XHTML is based on XML, HTML is SGML-based. They resemble the two halves of a single coin. To comply with XML standards, HTML was transformed into XHTML. Therefore, XHTML is more rigid than HTML and forbids users from getting away with mistakes in coding and structure