configuration database". As I understand it, it is based on the Configure extension and is extended so that it has all the functionality needed by the Wikimedia Foundation.
The things that excites me is that when more functionality actually makes use of a database of configurations, it will become possible to actually use different configurations when testing. As it is, the MediaWiki Testing Environment is at this moment very much about setting up an environment ready for testing. With configurations available in a database it is possible to test using these configurations. This makes for even more flexible testing.