HTTP (Hypertext Transfer Protocol) is the foundation of data exchange on the Web, operating as a request-response protocol between clients (browsers, apps) and servers. Defined in RFC 9110 and preceding standards, HTTP enables communication through methods, status codes, and headers that control how resources are requested, delivered, cached, and secured. Understanding HTTP means understanding how the modern internet works — every API call, webpage load, and data transfer relies on this protocol. A critical distinction: HTTP itself is stateless — each request is independent, requiring mechanisms like cookies or tokens to maintain state across interactions.