What is an ad group?

An ad group contains one or more ads that share similar targets. You set a bid, or price, to be used when an ad group’s keywords trigger an ad to appear. This is called a cost-per-click (CPC) bid. … Use ad groups to organize your ads by a common theme, such as the types of products or services you want to advertise.

For More Information Please Refer: https://support.google.com/google-ads/answer/2375404?hl=en