Thread:Extension talk:Wikibase Client/Wikibase? Wikibase Client? Wikidata build? huh? what?

As I understand it
 * Wikibase = awesome technology
 * Wikidata = site running that technology to provide millions of facts about items on Wikimedia projects
 * Wikibase Client = lighterweight code for other wikis in the cluster that want to use facts from wikidata.

None of this is apparent wondering around

Meanwhile this page has

but this extension is not obsolete, it's in use on tons of Wikimedia wikis (but not mediawiki.org).

I think
 * if you want to develop, check out Extension:Wikibase and follow instructions
 * if you want to see how WMF configures the site https://wikidata.wikimedia.org, check out Extension:Wikidata build and wander around in the operations/mediawiki-config repo, primariy in wmf-config/Wikibase.php

I still can't figure out what Wikibase Client is.