Which concept pertains to cloud customers paying only for the resources they use and consume, and only for the duration they are using them?

Measured service is a fundamental characteristic of cloud computing, meaning that cloud resource usage is monitored, controlled, and reported, providing transparency for both the provider and consumer. This enables a pay-per-use model, ensuring customers are billed only for the specific resources they consume and for the duration they are actively using them.

Auto-scaling is the ability to automatically adjust computing capacity to meet changes in demand, not directly about the billing model.

Portability refers to the ability to move applications and data between different cloud environments or between on-premises and cloud environments.

Elasticity is the ability to rapidly and elastically provision and de-provision computing capabilities to scale resources up or down quickly based on demand.