Directive (EU) 2019/944 of the European Parliament and of the Council of 5 June 2019 on common rules for the internal market for electricity and amending Directive 2012/27/EU.
Commission Implementing Regulation (EU) on interoperability requirements and non-discriminatory and transparent procedures for access to metering and consumption data, page 2, para (4)., page 1-2, para (3), article 2(1)