What is HTTP?

When a user selects a hypertext link, the client program on their computer uses HTTP to contact the server, identify a resource, and ask the server to respond with an action. The server accepts the request, and then uses HTTP to respond to or perform the action.

For example, when you select any of the following underlined hypertext links, you are identifying a particular resource, and asking the server to send it back to your computer in a format that your computer can display.