An agent or interface that enables changes to Identity data to be collected from trusted sources in near real-time and made available (published or subscribed) to identity directories or other systems. For example; details of a new employee published by the HR application to the Identity repository, for the purpose of provisioning. Some interfaces are termed "cagent-less" when they don't use a permanent connection between sources; instead they acquire the most up-to-date identity information only when it is required (ie event-based), usually by prior indexing or schema matching of the sources of the data; this is the way a 'virtual directory' work.
Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html