Application Programming Interface — a set of rules and endpoints that allow different software systems to communicate. Web APIs typically use HTTP methods (GET, POST, PUT, DELETE) to exchange data in JSON format.

The modern browser API for making HTTP requests. fetch() returns a Promise that resolves to the Response object. It replaces the older XMLHttpRequest (XHR) and works with async/await.

Standard request methods that indicate the desired action on a resource. GET retrieves data, POST creates, PUT/PATCH updates, DELETE removes. Each method has semantics about safety and idempotency.