PIFI is defined in Securities and Exchange Commission (SEC), Final Rule: Privacy of Consumer Financial Information (Regulation S-P) 17 CFR Part 248 (2000). Available at: https://www.sec.gov/rules/final/34-42974.htm

Both the GLBA and the regulations define NPI[5] in terms of PIFI.
The GLBA does not define PIFI but the FTC regulations define the term to mean any information:
(i) A consumer provides to you [the financial institution] to obtain a financial product or service from you;
(ii) About a consumer resulting from any transaction involving a financial product or service between you and a consumer; or
(iii) You otherwise obtain about a consumer in connection with providing a financial product or service to that consumer.