Anonymization. The conversion of data from something which is personally identifying and has meaning into another form which can not be reversed or traced back to the original source.
SHA256("email@example.com") => "2533d1b2cab8476f9e0c7226e027a013942c2aa3990443113939a3081ea8e1a6"
The intent of using anonymization is to hide the source data, but make it easy to know if one source data matches another.
Often anonymization will use a private Cryptographic Salt to prevent non-anonymized data from being easily matched to anonymized data.