Good question, isn’t it? As often as “cloud” is used in the media and by various providers, one would think that there is a clear definition of the cloud; but far from it, cloud is a term that describes the minimum requirements of a system, but does not allow for a concrete statement regarding the specific technology used. Incidentally, there is also no concrete agreement on these minimum requirements…
The cloud initially only describes a form of virtualization (abstraction of the physical layer) for the operation of a server infrastructure in order to effortlessly replace hardware or add further servers as needed—this cloud is also called IaaS (Infrastructure as a Service). However, the term cloud is also used for PaaS (Platform as a Service) or SaaS (Software as a Service). Here, too, the goal is to abstract the underlying layer; with PaaS, an operating system including settings is provided for the ad-hoc operation of applications (frequently used by developers), while with SaaS, access to a specific application is offered—for example, a webmail account.
Whether a service provider virtualizes and automates their products or not is essentially only their concern—the service provided (server instance, OS, or application) is, from the user’s perspective, no different than if it were not virtualized. From the user’s perspective, it is much more important to be clear about the possible consequences of using a cloud, especially if the provider does not host in the same country, if the hosted data requires special protection, if system availability plays a special role, etc. On the other hand, the costs of operating in-house must be weighed against this. As is so often the case, one cannot move forward without a compromise…
Hardware that is becoming increasingly affordable while performance increases, combined with the virtually nationwide availability of broadband connections, has led to the emergence of numerous clouds with a wide variety of offerings, and the Software as a Service sector is growing the fastest worldwide, as the services are also aimed at consumers.
As of today, however, web hosting companies still largely offer “PaaS” products, i.e., simple storage space on which, for example, a web application can be stored and operated by the customer. Only recently has there been a gradual shift to SaaS, mostly with self-developed, purchased, or leased website builder applications.
By the way, there is a detailed explanation of the cloud on Wikipedia…
