As “cloud computing” is gaining on its rivals in the race for the hottest IT buzzword du jour, I started noticing that many products that only yesterday were marketed as “hosting,” “grid” or “cluster” became “clouds” virtually overnight.
I realized something the other day. For something to call itself a computing cloud it is necessary, but not sufficient, for it to have no computing resources assigned permanently to a particular user and offer all resources to its users from a shared pool of resources. The permanent assignment in this context can usually be associated with words “provisioning” or “signup.” If a customer signup process includes or is immediately followed by a provisioning step (even if it happens behind the scenes), it’s not a cloud. This means that your regular hosting is not a cloud - you get a physical box, or a part of physical box, and it’s yours till it goes down or you stop using the service. Amazon EC2 on the other hand is definitely a cloud -your instance runs somewhere, and as long as it is running, this resource is yours. Once you shut it down, this resource goes back to the pool.
CORRECTION: Amazon EC2 satisfies this condition. But based on this info alone, technically speaking, it's impossible to say if it's a cloud or not, because I only provided a necessary condition.