The processing of personal data in such a manner that the personal data can no longer be attributed to a specific data subject without the use of additional information, provided that such additional information is kept separately and is subject to technical and organisational measures to ensure that the personal data are not attributed to an identified or identifiable natural person.
What differs pseudonymisation from anonymisation is that the latter consists of removing personal identifiers, aggregating data, or processing this data in a way that it can no longer be related to an identified or identifiable individual. Unlike anonymised data, pseudonymised data qualifies as personal data under the General Data Protection Regulation (GDPR). Therefore, the distinction between these two concepts should be preserved.
REGULATION (EU) No 536/2014 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 16 April 2014 on clinical trials on medicinal products for human use, and repealing Directive 2001/20/EC (art 4)
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32014R0536
