The Provisioning Service is an event and messaging service that can notify interested services about events in the LDAP directory service. When data changes in the LDAP directory on the Primary Directory Node, the Provisioning Service receives a notification about the change and notifies any subscribed services about the change. In contrast to the Univention Directory Listener, it provides the UDM representation of the change objects instead of the LDAP representation.
For more details refer to the official UCS Provisioning Service documentation and the Nubus Customization and Modification Manual.