MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 1: Overview of OLE DB
Enumerators are COM objects that search for available data source objects and other enumerators. Consumers that are not customized for a particular provider can use enumerators to search for an appropriate data source object to use.
An enumerator object exposes the ISourcesRowset interface, which returns a rowset describing all data source objects and enumerators that are known to the enumerator. A root enumerator, shipped in the MDAC SDK, traverses the registry looking for data source objects and other enumerators. For more information about the root enumerator object, see "Root Enumerator Object" in the OLE DB Core Components documentation. Other enumerators traverse the registry or search in a provider-specific manner. For example, an enumerator over the file system might search for subdirectories.