An ad unit is a specific ad placement or format within an app — the container an ad renders in, and the thing you actually monetize. A publisher typically runs several ad units across different screens and moments, each price-optimized through an [[ad-mediation]] layer that auctions every impression.
Format choice is one of the largest in-app monetization levers, because each trades revenue against user-experience cost differently:
The main mobile ad-unit formats
| Ad unit | What it is | Revenue / UX trade-off |
|---|---|---|
| Rewarded video | Opt-in video; the user gets an in-app reward | High eCPM + opt-in — best UX-to-revenue ratio |
| Interstitial | Full-screen ad at a natural break | High eCPM but interruptive — pace it carefully |
| Banner | Small persistent strip (usually bottom) | Low eCPM, low friction, steady fill |
| Native | Ad styled to match app content / feed | Moderate eCPM, best UX blend when done well |
| App-open | Shown on launch / resume | High eCPM but risky — can feel intrusive |
| Offerwall | List of reward-for-action offers | Niche; strong for reward-economy apps |
Most apps run a layered mix — rewarded video as the monetization core, interstitials at natural breaks, banners for steady baseline fill — all arbitrated by a mediation layer.
Format also shapes ad quality: [[viewability-rate]] and [[brand-safety]] expectations differ by unit, and rewarded/native units carry less accidental-click risk than banners or app-open ads. Optimize the mix per app by testing eCPM and retention impact together — a high-eCPM interstitial cadence that hurts [[retention]] can be net-negative on LTV.