License

This is just one person's research and not official documentation. Original source: phab:T284097#7376790.

Almost all content of almost all Wikimedia projects is dual-licensed under CC BY-SA 3.0 and GFDL (according to Terms of Use § Licensing of Content). The projects migrated from GFDL to CC BY-SA 3.0 in 2009 (Licensing update), because GFDL has some annoying requirements, but despite that, new contributions are still required to be made available under GFDL.  

There are several projects that are exceptions:

There are also several kinds of content that are exceptions:

  • Content of Wikidata main namespace, Property, Lexeme and EntitySchema namespaces is available under CC0 (https://www.wikidata.org/wiki/Wikidata:Copyright)
  • Content of Wikimedia Commons structured data about files is available under CC0 (I'm struggling to find a page that clearly documents this…)
  • Content of MediaWiki.org help namespace is available under CC0 (https://www.mediawiki.org/wiki/Project:PD_help)
  • Files uploaded to all wikis are available under a variety of licenses, as specified in each file's description
  • Tabular data and map data on Wikimedia Commons in the Data namespace is also available under a variety of licenses. Each piece of content documents this with the license attribute (by default CC0).
  • (there may be others)