HTML is a Language while HTTP is a Protocol.
HTML tags are used to help render web pages. The Hypertext Mark-up Language (or HTML) is the language used to create documents for the World Wide Web.
HTTP (Hypertext Transfer Protocol) is a protocol for transferring the hypertext pages from Web Server to Web Browser. HTTP is a generic and stateless protocol which can be used for other purposes as well using extensions of its request methods, error codes, and headers. Basically, HTTP is a TCP/IP based communication protocol, that is used to deliver data (HTML files, image files, query results, etc.) on the World Wide Web.