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.

Representational State Transfer — an architectural style for designing networked APIs. RESTful APIs use HTTP methods to perform CRUD operations on resources identified by URLs. Responses are typically JSON.

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.