What is a default bid?
A default bid can be set to apply to all Sponsored Search keywords in an ad group. For each Sponsored Search keyword, you can either use the default bid or specify a custom bid that is unique to that keyword. To help simplify bid management, you can use the default bid for most of your keywords (keywords that you feel comfortable managing as a group) and specify custom bids for a smaller set of keywords. You can easily reset the bid for all of the keywords with default bids at once simply by updating the default bid. You cannot specify a custom bid for Content Match at the keyword level. Rather, the Content Match bid that you set applies to all Content Match keywords in the ad group. Note: When campaign optimization is on, you may use the default bid limit. The default bid limit is the maximum price that you are willing to pay for a click. Learn more about Setting an Ad Group Default bid.