2.2 Overview of OLE/COM and the Functional Developer API
2.2.6 Type information and type libraries
COM uses type information to make formal descriptions of COM objects and their interfaces. Type information encodes such details as the names of interfaces, the GUIDs that identify them, their methods, and their methods' argument names and types.
With type information, all the interfaces that a COM object implements, and all the methods and properties of those interfaces, can be described in a way that client software can understand. Clients can use type information to determine how to communicate with COM objects, and to make decisions about whether to use them.
Clients get hold of type information through a type library. A type library is a representation of the type information for a COM object that client software can query to find out about the object's interfaces.
How does type information become a type library? As a server's developer, you enter the COM type information as part of the server's object and interface definitions. Functional Developer takes care of gathering the information into a type library, creating the library file, and installing it in the Windows Registry. This all happens as part of Functional Developer's server self-registration facilities.