CPA (Cost Per Action/Acquisition) marketing is a performance-based advertising model where affiliates earn a commission only when users complete a specific, desired action, like making a purchase, filling a form, signing up for a trial, or downloading an app, making it a cost-effective way for advertisers to pay for actual results, not just clicks or impressions. It's a form of affiliate marketing that incentivizes marketers to drive valuable conversions, benefiting both businesses seeking ROI and affiliates earning based on tangible outcomes.