CPA marketing is a type of online advertising where advertisers pay publishers for specific actions taken by visitors to the publisher's website, such as filling out a form or making a purchase. Advertisers set a specific budget and bid on the cost per action they are willing to pay, while publishers drive traffic to the advertiser's landing page. CPA marketing allows advertisers to pay only for the results they receive, making it a cost-effective and results-driven approach to online marketing. However, careful monitoring is required to ensure desired outcomes are achieved.