Which description of the purpose of an API is true?

While APIs can be used in authentication processes, their general purpose is not limited to providing a secure platform for internal user authentication; they facilitate broader inter-application communication.

APIs provide an interface to use an application's features, but they do not typically expose the underlying source code for developers to understand; instead, they abstract it.

An API's primary purpose is to expose specific functionalities or data of an application so that other applications can programmatically access and utilize them without needing to understand the internal workings. This allows for integration and interaction between disparate software systems.

While some APIs might be part of larger software development kits (SDKs) or frameworks, an API itself is not a framework but rather a set of definitions for how to interact with a service or application.