Wikimedia engineering refers to the engineering and product development staff employed by the Wikimedia Foundation. Its mission is to build, improve and maintain the technical infrastructure of Wikimedia projects (software and hardware), by supporting and complementing volunteer efforts.
The Wikimedia Foundation Platform Engineering team is responsible for the MediaWiki core, managing work from volunteer developers, as well as for providing services that are used by multiple technology teams.
The Operations team is responsible for the technical infrastructure of Wikimedia sites: this includes the data centers, servers and network. They document most of their work on the wikitech wiki. Also:
Wikimedia Labs — A test environment using virtual machines for testing and experimentation