What is the difference between HTTP and HTML?

HTML is a description "language" for how to present information that passes via http, HTML stands for Hyper Text Markup Language and has multiple "versions" that change as our use of the world wide web changes.

Hyper Text Transfer Protocol, http, is a computer protocol or set of procedures, describing how computers may pass information in an orderly fashion. The great thing about http is it is not just related to one single protocol but is built to deal with a conglomeration of many protocols allowing different things to be handled easily in one well known package.

Http says how to pass the info, HTML says how to organize the raw data and present it at the other side.

HTML is one of many markup languages (SGML, XHTML, DHTML...) but is the most used as it was the one chose to present info over the world wide web.