Cost per subscriber for a cloud service provider reduces with the increase in number of subscribers. It is a public cloud service. Can you identify what this would be called?

Consumption-based billing is a payment model where customers pay only for the resources they use, but it doesn't explain the provider's underlying cost structure efficiency.

Operational expenditures (OpEx) are ongoing costs for running a business, like utility bills or salaries, but this term doesn't specifically describe the cost reduction due to increased volume.

Scalability is the ability of a system to handle a growing amount of work by adding resources, which is a characteristic of cloud computing, but it doesn't describe the cost reduction per unit with increased volume.

Economies of scale refer to the cost advantage that arises with increased output of a product, in this case, cloud services. Cloud providers can offer lower prices per unit as they serve more customers because their fixed costs are spread over a larger customer base, making the cost per subscriber reduce.