API

An API (Application Programming Interface) is a standardized set of classes, interfaces and annotations providing a facade by which a Framework or library provides services/features. It can be seen as a usage contract for services between developers and users. Enterprise stacks provide through all their Frameworks a coherent set of APIs.

In the Java world, these APIs are often available through their javadoc (software provided by Oracle that reads the source code and produces HTML documentation reflecting the API).