Geo-targeting exclusion, also called reverse geo-targeting refers to the possibility of defining a geographic area (or several areas) where ads must not be displayed.
It is mainly used for AdWords campaigns but it may also be theoretically used for "traditional" display campaigns.
The goal may be to exclude some areas where a brand has no retail stores or to manage channel conflicts.
Geo-targeting exclusion may also be used by some rogue affiliates which practice trademark poaching. In this case, they usually exclude area matching merchant and affiliate network headquarter locations. Thus, merchant and network marketing teams working at headquarters can’t see the forbidden ads.