Ad verification is a process which attempts to verify that a campaign has executed according to the agency’s or advertiser’s choices and exclusions. These choices and exclusions can relate to:
targeted audience
geotargeting
webplanning
ad placement
brand safety
competitive separation
page or site context
day parting
...
The IAB ad verification guidelines addresses five primary service lines of ad verification:
Site Context
Geo-Targeting
Ad Placement
Competitive Separation
Fraud Detection: click fraud and impression fraud
Other service lines can be addressed by ad verification vendors:
Audience verification
Ad viewability measurement
....
Ad verification is made in real time and can generate alerts to agencies or publishers. Based on this alerts agencies can remove "bad" publishers during the campaigns.
Ad verification is used by advertisers, agencies but also by ad networks / exchanges for managing and controlling their networks and reassuring advertisers.
See also brand safety.
The evolution of ad verification (image credit Adometry):