Public-domain dedication. The author waives all copyright and database rights to the extent permitted by law.
CC0 1.0 is not a licence — it is a dedication of work to the public domain. The author waives all copyright, database, and related rights to the maximum extent permitted by applicable law, with a fallback licence in jurisdictions where dedication to the public domain isn't legally possible.
CC0 is the standard recommended dedication for open data because it removes attribution-driven friction from large-scale data combination. Significant open-data publishers including Europeana, the British Library, and several US federal agencies have used CC0 specifically to eliminate the attribution-stack problem that arises when combining many CC-BY-licensed datasets.