REST
also called RESTful API
An architectural style for APIs built on resources identified by URLs, manipulated with uniform HTTP methods, and stateless requests.
The parts that carry practical weight: resources not actions (/orders/123, not
/getOrder?id=123), uniform methods with their standard semantics — GET safe and cacheable,
PUT and DELETE idempotent, POST neither — and statelessness, meaning any instance can serve
any request, which is what makes horizontal scaling trivial.
Getting the status codes right is not pedantry, it is the contract: 400 means the client must change something, 500 means it may retry, 409 means a conflict it must resolve, 429 means slow down. Clients build retry logic on these.
Most real APIs are "REST-ish" and that is fine. The strict interpretation including hypermedia (HATEOAS) is rarely implemented and rarely missed. What is genuinely worth keeping is predictability: a consumer who knows the resource can guess the URL and the method.