public cloud, private cloud, and fuzzy cloud demarcation

Public/private and internal/external are two separate dimensions. Public, private, or community attributes specify how widely the cloud service is shared; a sharing dimension. Internal or external denote the consumer’s view of the Cloud’s service interface. The view is associated with a consumer’s responsibility for service development, operations, and management; a responsibility dimension. A third dimension, on-premise or outsourced, describes where the service assets are located; a location dimension. Many architects conflate the three dimensions. NIST has recently published a Cloud Computing Reference Architecture which spends considerable prose disentangling the concepts. According to NIST:

A private cloud gives a single Cloud Consumer organization the exclusive access to and usage of the infrastructure and computational resources. It may be managed either by the Cloud Consumer organization or by a third party, and may be hosted on the organization’s premises (i.e. on-site private clouds) or outsourced to a hosting company (i.e. outsourced private clouds).

Let’s run through three quick use cases describing public, private, and community:

1. A public cloud service is accessible to any consumer. For example, all organizations who have sales teams.
2. A private cloud service is accessible to only members of a single team. For example, a custom tailored Enterprise Resource Planning application delivered as a service to company employees.
3. A community cloud blends the two access models. A community cloud service is accessible to a select, exclusive group. For example, a classified information service delivered to government agencies

A person or organization will often use and deliver cloud services across private, public, and community environment. A hybrid cloud strategy delivers, spans, and connects clouds across all dimension attributes. According to NIST,

A hybrid cloud is a composition of two or more clouds (on-site private, on-site community, off-site private, off-site community or public) that remain as distinct entities but are bound together by standardized or proprietary technology that enables data and application portability.

Source:https://blog.cobia.net/cobiacomm/2013/10/18/public-cloud-private-cloud-and-fuzzy-cloud-demarcation/