Backfill

Backfill refers to the secondary or tertiary ad demand sources used when the primary demand source (your main ad network) doesn't fill an impression. For example, if Mediavine can't find a buyer for a particular impression, a backfill source like AdSense might serve an ad instead.

Good backfill strategy ensures you're never showing blank ad slots. Most premium networks handle backfill automatically through their header bidding setup. If you manage your own ad stack, configure backfill partners in your ad server (like Google Ad Manager) as lower-priority line items that only serve when primary demand is exhausted.