Pseudonymisation means that personal data is replaced by a licence plate (e.g. through a user ID), so that the direct reference to the person can be is no longer possible without further ado - but basically recoverablee.g. through additional information.
In contrast to the Anonymisation pseudonymised data processing is still subject to the GDPR, as it is still technically possible to establish a personal reference.
In the Website Analytics pseudonymous user IDs are often used to recognise returning visitors - without direct identification. Such data must nevertheless be protected and may only be processed with the appropriate legal basis.
