The cost-per-click bid is the cost per click you are willing to pay when someone clicks your ad.
Your cost per click may actually be lower than your cost-per-click bid. Remember, never bid more than you are willing to pay for a click. For Sponsored Products, selecting the Dynamic bids - up and down bidding strategy may cause some bids to exceed your cost-per-click bid. Learn more about bidding strategies
The maximum default bid is the cost per click you are willing to pay when someone clicks an ad from the ad group. This bid will apply to all clicks unless you have set a customized bid for an individual keyword in this campaign or ad group.
Setting custom cost-per-click bids is optional. You can use the ad group maximum default bid, or you can create custom bids for specific targets in your ad group. Keyword bidding gives you the most control in terms of your ad performance and spend. Cost-per-click bids that are set at the keyword level take precedence over the default cost-per-click bid set at the ad group level. To set a cost per click for a specific keyword, select the ad group that contains the keyword and select the Keyword tab. In the column labeled Max. Default Bid enter the maximum cost-per-click you are willing to pay for that keyword.
The maximum bid is the cost-per-click that you are willing to pay when someone clicks an ad from this ad group. You can change the maximum bid at any time by selecting the Targeting tab. This bid will apply to all clicks unless you set a customized bid for an individual targeting group in this ad group.