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Cloud computing supplies configurable computation resources through a computer network, drawing on a shared pool that users can obtain and release with little provider intervention. The NIST definition distinguishes five characteristics: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service. Together these describe how capacity is requested, shared, scaled and accounted for.^[ref]

For example, a group running a numerical simulation can request several virtual machines, execute independent runs, save the results and release the virtual machines. Rapid elasticity concerns changing allocated capacity as demand changes; measured service records usage such as processor time or storage. A physically distributed system can have a single operator: physical distribution and administrative control answer different questions.

Measured service is the cloud-computing characteristic in which resource use is monitored, controlled and reported through metering appropriate to the service. Examples include processor-hours, stored bytes, network transfer and active accounts. Metering makes usage visible to the provider and consumer; it does not require one universal billing formula.^[ref]

For example, a batch of simulations can record the number of machine-hours consumed independently of the number of simulations completed. A failed run may still consume resources. Selecting a meaningful unit therefore requires distinguishing allocated capacity, elapsed use and delivered work. These measurements support accounting and capacity decisions without by themselves measuring the scientific value or correctness of the results.

Peter Mell coauthored The NIST Definition of Cloud Computing by Peter Mell and Timothy Grance in 2011. The publication identifies on-demand self-service, broad network access, resource pooling, rapid elasticity and measured service as essential characteristics.^[ref]

The classification separates what service a consumer controls from how it is deployed. Infrastructure, platform and software services expose different management boundaries, while public, private, community and hybrid deployments describe organizational arrangements. A service can therefore be publicly accessible without giving its consumers control of the underlying operating systems.