Cloud computing is the delivery of information technology services over a network, usually the internet. In the cloud computing model, infrastructure, data, and software are hosted by the vendor and delivered to the user as a service, much like a utility company would deliver water or electricity.
According to the official NIST definition, there are five essential characteristics of cloud computing: on-demand self-service provisioning of resources, broad network access, resource pooling, rapid elasticity, and measured service.
The three main cloud computing models are infrastructure as a service, software as a service, and platform as a service.
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