There are some differences between html and xhtml.
HTML is an acronym for Hypertext Markup Language. It is a document markup language that allows the author to present content in a structured manner, using codes like headings, paragraphs, lists, images, video and more.
XHTML is an acronym for XML HTML. XML HTML is an extension of HTML that allows for greater structuring of the document with enhanced capabilities for coding and defining the document
XHTML is for Extensible Hypertext Markup Language. It has considered as a part of the XML markup language this is because of XHTML have features of both XML and HTML.
HTML is the Hypertext Markup Language which is the most widely used language on the internet. HTML has used to create web pages and link them from one to another.
XHTML has developed to make HTML more extensible and adaptable to work with other data formats (such as XML).
HTML is not a programming language, it is a markup language.