Cost per action (CPA) is a pricing model where advertisers pay for specific actions, such as a purchase or sign-up, rather than for clicks or impressions. CPA provides more control over ad spend by tying costs directly to campaign outcomes.

CPA is popular for performance-driven campaigns, as it focuses on measurable results. By optimizing for CPA, advertisers can maximize ROI and ensure that the budget is spent only when a valuable action occurs.