Hypertext Transfer Protocol (HTTP) is the communication method for transferring data on the web. It is defined by the [http://www.ietf.org/](Internet Engineering Task Force), and the most recent spec is defined by RFCs 7230, 7231, 7232, 7233, 7234, and 7235.
Anything interacting with a web server (e.g. browsers and CDNs) does so via HTTP. HTTP response headers should be set to employ a caching strategy. See HTTP Caching for an introduction to these techniques.