When research data include personal data, privacy issues can occur resulting in need to avoid the presence of personal identifiers in datasets.
Anonymous information are information which does not relate to an identified or identifiable natural person, or personal data rendered anonymous in such a manner that the data subject is not or no longer identifiable.
There are different ways to convert personally identifiable information into aggregated data, that may or may not be able to be re-associated with the initial personal data at a later time.
Different research fields (e.g. health sciences, social sciences) can have specific standard, tools and procedures for anonymization of personal data.
You can find a general reference about the Research Data Management in the the RDM Policy