Definition
Means any natural or legal person established in the Union explicitly designated to act on behalf of a digital service provider not established in the Union, which may be addressed by a national competent authority or a CSIRT instead of the digital service provider with regard to the obligations of that digital service provider under this Directive
Source
Point (10) of Article 4 of Directive (EU) 2016/1148 of the European Parliament and of the Council of 6 July 2016
Link
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32016L1148&rid=1