What Is HTTP?
Hypertext Markup Language (HTML) is the language used to describe the insides of Web documents, Hypertext Transfer Protocol (HTTP) is the language used to describe how these documents are sent over the Internet.
HTTP prescribes the rules by which browsers make requests and servers supply responses. This set of rules, or protocol, includes ways to
Ask for a document by name
Agree on the data format
Determine who the user is
Decide how to handle outdated resources
Indicate the results of a request and other useful functions.
HTTP consists of a set of commands written as lines of ordinary ASCII text. When you use a Web browser, you don’t enter the HTTP commands directly. Instead, when you type a URL or click a hyperlink, the browser translates your action into HTTP commands that request the document from the server specified in the URL. The Web server finds the document and sends it back to the browser, where it’s displayed, along with its associated graphics and other hyperlinks.
The HTTP Specification
Internet standards are usually specified in a Request for Comments (RFC) published by the Internet Engineering Task Force (IETF). These RFCs are widely accepted by the Internet research and development community. Because they’re standards documents, they tend to be written in a formal language, like that of a legal document. This makes them unsuitable as tutorials, but invaluable for reference. RFCs are numbered and never change when issued. If a standard is updated, a new RFC is issued. Being standards, RFCs are widely available on the Internet.
Several RFCs deal with HTTP :
RFC 1945 A description of HTTP version 1.0
RFC 2068 The initial description of version 1.1
RFC 2616 An updated version of the 1.1 specification
Source :- JSP: The Complete Reference By Phil Hanna