None of the above. The Enterprise Library is a higher level abstraction for .NET functionality.
For example the Data Access Application block within the Enterprise Library wraps most of ADO.NET to provide a simpler implementation of data access.

Ultimately, these application blocks could be used by business objects, WinForms and more but they are not designed to create these application artifacts in and of themselves. Frameworks like MM.NET usually incorporate similar application block patterns into an even higher level of abstraction that includes business objects, business rule objects, controls with built in binding (similar to MS Access), and more.

Right from the introduction:
Application blocks help address the common problems that developers face from one project to the next. They have been designed to encapsulate the Microsoft recommended best practices for .NET applications. They can be added into .NET applications quickly and easily. For example, the Data Access Application Block provides access to the most frequently used features of ADO.NET in simple-to-use classes, boosting developer productivity. It also addresses scenarios not directly supported by the underlying class libraries. (Different applications have different requirements and you will not find that every application block is useful in every application that you build. Before using an application block, you should have a good understanding of your application requirements and of the scenarios that the application block is designed to address.)

The application blocks that comprise the Enterprise Library are the following:

Caching Application Block allows developers to incorporate a local cache in their applications.
Configuration Application Block allows applications to read and write configuration information.
Data Access Application Block allows developers to incorporate standard database functionality in their applications.
Cryptography Application Block allows developers to include encryption and hashing functionality in their applications.
Exception Handling Application Block allows developers and policy makers to create a consistent strategy for processing exceptions that occur throughout the architectural layers of enterprise applications.
Logging and Instrumentation Application Block allows developers to incorporate standard logging and instrumentation functionality in their applications.
Security Application Block allows developers to incorporate security functionality in their applications. Applications can use the application block in a variety of situations, such as authenticating and authorizing users against a database, retrieving role and profile information, and caching user profile information.