A means of identifying a natural person or data subject by associating informational traces an individual leaves when operating online. Examples of online identifiers may include social media account handles or usernames, device fingerprints, pixel tags, MAC addresses, and advertising identifiers. In some jurisdictions, online identifiers are known as internet identifiers.

The definition and permissible uses of online identifiers may vary by jurisdiction. The General Data Protection Regulation (GDPR), for example, includes online identifiers in its personal data definition (Article 4(1), GDPR).

Online identifiers under the GDPR include:

(Recital 30, GDPR.)

For further information, see Practice note, Overview of EU General Data Protection Regulation: Online Identifiers.