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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.

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.

Rapid elasticity is the ability to provision and release computing capacity quickly in response to demand, often automatically. The consumer may experience capacity as readily available even though the provider operates finite physical resources.^[ref]

For example, a service can add workers when its queue grows and remove them after the backlog clears. A control rule needs an observation signal, a scaling policy and time for new workers to become ready. Elastic capacity does not make every program parallel: a serial bottleneck, shared database or slow startup can prevent additional workers from increasing throughput. Releasing capacity also requires preserving needed state outside workers that may disappear.

Timothy Grance coauthored the 2011 NIST definition of cloud computing with Peter Mell. It specifies five essential characteristics, service models and deployment models rather than equating every remotely accessed computer with a cloud.^[ref]

For example, rapid elasticity concerns provisioning and releasing capacity as demand changes; it is distinct from resource pooling, which concerns sharing provider resources among consumers. A manually provisioned remote server can lack the on-demand and elasticity characteristics. Separating these properties makes system descriptions more informative than simply attaching a cloud label.