Basics

HTTP ( Hypertext Transfer Protocol ) is an application-layer protocol for transmitting hypermedia documents, such as HTML. It was designed for communication between web browser ( client ) and web server ( server ), but it can be used for another purposes. Client opens an connection, ready to make a request, then waiting it until it recives a response.

HTTP is generally designed to be simple and human readable. Even in HTTP/2, it was more complex by encapsulating the HTTP messages but it still can be read and understood by human.

Introduced in HTTP/1.0, HTTP headers made this protocol easy to extend and experiment with. That's why HTTP is extensible.

HTTP is stateless. It means that there is no link between two requests being successively carried out on the same connection.