Pure-reference catalog of data-masking techniques and de-identification privacy models. Enumerates the seven canonical masking operators (substitution, shuffling, number/date variance, encryption, hashing, nulling, masking-out / character-scrambling) plus tokenisation, redaction, format-preserving encryption, and Microsoft Presidio's six built-in operators. Distinguishes reversible techniques (pseudonymisation candidates per GDPR Art. 4(5)) from irreversible techniques (anonymisation candidates), and maps them to NIST SP 800-188 privacy models - k-anonymity, l-diversity, t-closeness, differential privacy (deep model definitions in references/). Cites ISO/IEC 20889:2018 for the standard taxonomy. Use to pick the right masking operator per field type and risk level.