Advertising to existing app users to bring them back or move them to an event, tracked by the MMP as a re-attribution or re-engagement. Depends on device identifiers, so it has shrunk on iOS since App Tracking Transparency.
Cite this entry:
Agency Echelon. "Re-Engagement." Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/glossary/re-engagement/