This is a legal term from the European General Data Protection Regulation (GDPR). The GDPR defines an Identifiable Natural Person (Article 4 (1)) as follows:
"an 'identifiable natural person' is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person;"
→ DEFINITIONS (ARTICLE 4 (1)) | GENERAL DATA PROTECTION REGULATION (GDPR)