Here's a sentence from the OPM website: Beginning June 8 and continuing through June 19, OPM will be sending notifications to approximately 4 million individuals whose Personally Identifiable Information was potentially compromised in this incident.
In fedgov speak Personally Identifiable Information (PII) is anything that could be used to identify an employee besides their name. The name is the key, and by itself is not PII, but anything with the name is - birth date, maiden name, address, phone number, ssn, mother/father/family information, marital status, sex, race, ethnicity, etc...
An address may not be PII. It depends... For example, if an agency sent you a letter, the name and address appearing together on the outside of the envelope would not be considered protected PII.