Wikipedia
De-identification is the process used to prevent a person’s identity from being connected with information. Common uses of de-identification include human subject research for the sake of privacy for research participants. Common strategies for de-identifying datasets include deleting or masking personal identifiers, such as name and social security number, and suppressing or generalizing quasi-identifiers, such as date of birth and zip code. The reverse process of defeating de-identification to identify individuals is known as re-identification. Several successful re-identifications attempts have purported to doubt on the effectiveness of de-identification in protecting individuals' privacy. A systematic review of the evidence found that published re-identification attacks were performed on data sets that were not de-identified properly (using recognized standards).
The United States President's Council of Advisors on Science and Technology and others have recently deemed de-identification "somewhat useful as an added safeguard" but not "a useful basis for policy" as "it is not robust against near‐term future re‐identification methods".