Target CPA bidding
Target cost-per-acquisition bidding has AdWords set bids to help get as many conversions as possible at the target cost per acquisition you set. tCPA does this by using your campaign conversion history and many signals about the auction to predict which clicks are likely to be valuable. Then tCPA adjusts your auction bids to get as many conversions as possible within your target acquistion cost.
Enhanced cost-per-click bidding looks for ad auctions that are more likely to lead to conversions and raises your max manual bid to compete harder for them. If a click seems less likely to convert, eCPC will automatically lower your bid by as much as 100 percent. eCPC will try to keep each keyword’s average CPC below the max CPC.
Target ROAS bidding:
Target return-on-ad-spend bidding automatically sets your bids to maximize your conversion value while trying to reach an average return on ad spend.