Bid and cost cap are two different bidding strategies used in online advertising campaigns. Bid refers to the maximum amount of money an advertiser is willing to pay for a click or impression on their ad. This bidding strategy is commonly used in pay-per-click (PPC) advertising, where the advertiser competes against other advertisers for ad placement. The higher the bid, the higher the chances of the ad being displayed. On the other hand, cost cap refers to the maximum amount an advertiser is willing to pay for a specific action, such as a conversion or a lead. This bidding strategy is commonly used in cost-per-action (CPA) advertising, where the advertiser pays only when a specific action is taken. The cost cap ensures that the advertiser does not overspend on a particular action, while still achieving their desired results. In summary, bid is for ad placement, while cost cap is for specific actions.