What is the difference between Anonymisation and Pseudonymisation?

Anonymisation and Pseudonymisation?

Pseudonymisation is processing data without expressly at that time being able to identify a particular person – essentially it is like identifying someone by a pen-name (pseudonym) or by a code name. Data is considered pseudonymous as long as the means to access the true identity of the individual is kept separately and subject to specific technical/structural measures to prevent the individual being identified or made identifiable.

Anonymised data is truly private as all identifying features (metadata) is removed making it impossible to identify a data subject. Recital 26 to the GDPR states that anonymised data is not personal data for the purposes of the GDPR:

The principles of data protection should therefore not apply to anonymous information, namely information which does not relate to an identified or identifiable natural person or to personal data rendered anonymous in such a manner that the data subject is not or no longer identifiable. 6This Regulation does not therefore concern the processing of such anonymous information, including for statistical or research purposes.

Recital 26, GDPR