NIST Definition

Berkeley Definition

Cloud computing refers to both the applications delivered as services over the internet and the hardware and systems software in the datacenters that provide those services.
The services themselves are called Software as a Service (SaaS).
The datacenter hardware and software is called Cloud.
Types of clouds,
- Public Cloud: A cloud that is made available to the public in a pay-as-you-go manner.
  - The service being sold here is called Utility Computing.
- Private Cloud: The internal datacenters of a business or other organization which are not made available to the public.
The terms Hardware as a Service (HaaS), Infrastructure as a Service (IaaS) and Platform as a Service (PaaS) are not precisely defined.