The cost is the amount of money that is required to pay for something. In the context of advertising, the cost can refer to the amount of money that is paid to an ad platform, publisher, or other party in exchange for displaying an ad. The cost of an ad can be based on various factors, such as the size of the ad, the format of the ad, the placement of the ad, and the audience that the ad is targeting. Advertisers typically aim to minimize the cost of their ads while maximizing their performance, and may use various strategies, such as bidding, targeting, and optimization, to achieve this goal.