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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.

On-demand self-service lets a consumer provision a computing capability when needed without requiring a human interaction with the provider for each request. The consumer might request server time or network storage through a portal or application programming interface.^[ref]

For example, an authorized research workflow can request a temporary machine, run an analysis and release it through automated calls. The provider can still enforce quotas, permitted configurations and account policy. Self-service describes how a request is fulfilled; it does not promise unlimited capacity or remove the need for authorization. Automating repeated provisioning makes temporary resources practical while leaving lifecycle and data-retention choices explicit.

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.