What are Web APIs?

Web APIs are the APIs implemented by browsers (e.g., Chrome, Edge, Firefox) that let JavaScript developers do things like make XHR requests, use Geolocation, use browser storage and so on. See here for the list of all the APIs available in most browsers.

You have several Web APIs (e.g., the Geolocation API) that give you access to various interfaces (object types) (e.g., Navigator).