Too Many Clouds

The cloud is the buzzword of the moment, unfortunately used in such a wide range of contexts that it can become misleading.

As a technology, and per the initial use of the term, the cloud refers mostly to the decoupling between software (services) and the physical hardware it runs on. In a cloud based architecture, you don't need to understand or even be aware of the physical infrastructure enabling a specific service. You access a services via a logical endpoint, and it's up to the cloud-technology to bridge your request to the proper "in-cloud" computing resources. In short, it can be easily be compared to a traditional computer cluster, but capable of grouping a massively larger and diversified set of components and providing a wider range of services.

As a service, int the enterprise IT infrastructure world, the cloud usually refers to an application or "virtual server" hosting service. An application hosting service usually supports a specific set of development frameworks, applications using such frameworks may be run with minimal adjustments to their build and deployment process. The virtual server hosting services, are usually powered by one of the many server virtualization technologies extended with the provider specific management tools.

As a service, in the "domestic" world, the cloud is usually a marketing term for internet based storage «which can be 'cloud' technology enable, or not». 

Clouds can either be public «using internet accessible components», private «using enterprise components)» or hybrid.