What is HTTP
HTTP stands for Hypertext Transfer Protocol. It is the communication model that lets a client ask a server for a resource and lets the server send a response back.
In backend engineering, HTTP is the foundation for web applications, REST APIs, and many service-to-service integrations. When you understand HTTP clearly, API design becomes much easier to reason about.
Client and Server
A client is the application making the request. This can be a browser, a mobile app, another backend service, or a command-line tool.
A server receives the request, decides how to handle it, and returns a response. The server may read files, run business logic, query a database, or call another service before responding.
Request and Response
An HTTP request describes what the client wants. It usually includes a method, a URL, headers, and sometimes a body.
An HTTP response describes what happened. It includes a status code, headers, and often a body containing data or an error message.
The request and response cycle is the smallest useful unit of backend communication.