Cost per app install, the standard buying and reporting unit for mobile app user acquisition. Since Apple's App Tracking Transparency framework, iOS installs are attributed mostly through SKAdNetwork and its successor AdAttributionKit, which report in aggregate and with delay, so CPI on iOS is an estimate rather than a count.
Related terms
Cite this entry:
Agency Echelon. "CPI." Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/glossary/cpi/