The Hypertext Transfer Protocol (HTTP) is an Application Layer protocol for distributed, collaborative, hypermedia information systems. You can perform Hypertext Transfer Protocol through a browser. For example, bring up Internet Explorer and type in http://example.com or http://www.example.com
HTTP is a request-response protocol standard for client-server computing. In Hypertext Transfer Protocol, a web browser, for example, acts as a client, while an application running on a computer hosting the web site acts as a server. The client submits HTTP requests to the responding server by sending messages to it. The server, which stores content (or resources) such as HTML files and images, or generates such content on the fly, sends messages back to the client in response. These returned messages may contain the content requested by the client or may contain other kinds of response indications. A client is also referred to as a user agent (or 'UA' for short). A web crawler (or 'spider') is another example of a common type of client or user agent.
In between the client and server there may be several intermediaries, such as proxies, web caches or gateways. In such a case, the client communicates with the server indirectly, and only converses directly with the first intermediary in the chain. A server may be called the origin server to reflect the fact that this is where content ultimately originates from.
Hypertext Transfer Protocol is not constrained in principle to using TCP/IP, although this is its most popular implementation platform. Indeed HTTP can be "implemented on top of any other protocol on the Internet, or on other networks." HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used.
Resources to be accessed by HTTP are identified using Uniform Resource Identifiers (URIs) or, more specifically, Uniform Resource Locators (URLs) using the http or https URI schemes.
Its use for retrieving inter-linked resources, called hypertext documents, led to the establishment of the World Wide Web in 1990 by English physicist Tim Berners-Lee.
The original version of Hypertext Transfer Protocol, designated HTTP/1.0, was revised in HTTP/1.1. One of the characteristics in HTTP/1.0 was that it uses a separate connection to the same server for every document, while HTTP/1.1 can reuse the same connection to download, for instance, images for the just served page. Hence HTTP/1.1 may be faster as it takes time to set up such connections.
The standards development of HTTP has been coordinated by the World Wide Web Consortium and the Internet Engineering Task Force (IETF), culminating in the publication of a series of Requests for Comments (RFCs), most notably RFC 2616, which defines HTTP/1.1, the version of HTTP in common use.