Personally Identifiable Information (PII) is any data that could potentially identify a specific individual. Any information that can be used to distinguish one person from another and can be used for de-anonymizing anonymous data can be considered PII. Examples include a full name, Social Security number, driver’s license number, bank account number, passport number, and email address.
The abbreviation PII is widely accepted in the U.S. context, but the phrase it abbreviates has four common variants based on personal / personally, and identifiable / identifying. Not all are equivalent, and for legal purposes the effective definitions vary depending on the jurisdiction and the purposes for which the term is being used. (In other countries with privacy protection laws derived from the OECD privacy principles, the term used is more often “personal information”, which may be somewhat broader: in Australia’s Privacy Act 1988 (Cth) “personal information” also includes information from which the person’s identity is “reasonably ascertainable”, potentially covering some information not covered by PII.)