The CPA model is at the core of performance-based campaigns, meaning all other performance models are derivative form of this model. Again, it is a pay-for-performance model where clients only pay for specific actions such as a sale, lead, or click.
The CPA model can be used in a variety of contexts, such as affiliate marketing, cost-per-lead (CPL), cost-per-click (CPC), and cost-per-impression (CPI) advertising.
This term is often used interchangeably with "cost-per-acquisition".