Anonymisation and pseudonymisation
Also known as: anonymised data · pseudonymised data · de-identification
Anonymisation makes re-identification reasonably impossible and takes the data outside the law; pseudonymisation merely replaces identifiers, and the data stays in scope.
The difference is legal, not cosmetic. A pseudonymised database is still a database of personal information: the mapping key exists somewhere, so the link does too.
True anonymisation is hard. Removing names is almost never enough: combining a postal code, a date of birth and a gender is often sufficient to re-identify someone in a dataset.
Pseudonymisation is nonetheless a recognised and recommended security measure — it reduces the impact of a breach even though it does not lift the obligations.
What it means for a small business
The costly mistake is announcing "our data is anonymised" in a privacy policy when it is pseudonymised. That is a verifiable claim, and a false one.
Related terms
So what actually applies to you?
A definition tells you what a term means, not what your organization must do. The assessment answers the second question — free, no credit card.
Updated September 1, 2026 · Educational definition; not legal advice.