Pixel Stuffing

Pixel stuffing happens when one or more ads of normal dimension, say 468 x 60, are compressed into a tiny 1×1 pixel frame on a publisher’s site. Every time a visitor lands on this website they will trigger an impression, even though the ad is virtually invisible to them. By reducing ads to only 1×1 pixel, bad actors can trigger impressions from a greater number of ads than they would legitimately be able to fit on a page.

Source: TrafficGuard Glossary