The Hypertext Transfer Protocol (HTTP) is a protocol that is ubiquitous on the Internet. All web traffic is transferred by HTTP, but HTTP is also used for web services. HTTP follows a simple request-response paradigm, and since HTTP is a stateless protocol, individual requests are not correlated. In order to introduce state, mechanisms like cookies need to be used.
Web servers operate typically on TCP port 80, web proxies operate typically on TCP port 8080. However, this is pure convention, HTTP can be run on ports with any port number. In this case the browser must be told to use the alternative port number by including the port number into the URL.
Use this tag for questions on programs and services that use HTTP. For questions specific to web servers the Server Fault Stack Exchange is probably more appropriate.