A set of campaigns that share a key performance indicator. Campaign groups are helpful for tracking the overall performance of multiple campaigns with similar goals.

• Set performance targets to designate numerical goals shared by all campaigns in a campaign group. 
• Monitor campaign group performance to see whether you’re on track to meet your performance targets. If not, you may consider adjusting your campaigns’ settings.
• You can create campaign groups with any combination of Search, Shopping, Display, or Video campaigns. 
• A campaign can be added to only 1 campaign group at a time. It can’t belong to multiple campaign groups.
• Campaign groups are optional—not every campaign must belong to a campaign group.  
• Any campaign using a shared budget cannot be added to a campaign group. 
• Removing a campaign from a campaign group will remove its performance data from the campaign group.
• Create, view, and edit campaign groups by clicking Campaign groups in the left navigation panel.

* Nguồn: Google