HTTP (HyperText Transfer Protocol) is the protocol that lets a client, usually a browser, request a resource from a server and receive its response; HTTPS is its encrypted, secure version.
The principle is simple: the client sends a request (a method such as GET to read or POST to send data, an address, headers), and the server replies with a status code (200 if all is well, 404 if the page does not exist, 500 for a server error) and content. HTTP keeps no memory from one request to the next: cookies and tokens are used to maintain a session.
HTTPS adds an encryption layer (TLS) that protects exchanges against eavesdropping and tampering. It has become the norm on the web.
HTTP is not only for web pages: most APIs are built on it. The protocol has evolved with HTTP/2 and then HTTP/3 to become faster.
Why it matters when hiring
For a back-end developer or a DevOps profile, understanding HTTP in depth (status codes, caching, headers, cookies, TLS) is not optional: it is the foundation for designing clean APIs and troubleshooting incidents. A simple interview question, what happens when I type an address into the browser, quickly reveals the real level.