What is personal data?

Personal information aka personal data or personally identifying information (PII), is the widely accepted abbreviation. The phrase it abbreviates has four common variants based on personal / personally, and identifiable / identifying

They all are not equivalent, and for legal purposes the effective definitions vary depending on the jurisdiction and the purposes for which the term is being used.

PII is defined as "any information about an individual maintained by an agency, including any information that can be used to distinguish or trace an individual's identity, such as biometric records, social security number, name, date and place of birth, mother's maiden name; and any other information that is linkable or linked to an individual, such as medical, financial, educational and employment information."
Under European the term "personal data" is significantly broader than in the US, and in EU this term determines the scope of the regulatory regime.