To me, a cloud is a distributed system of computing resources where the resources can be dynamically allocated with an API. A hosted application should be able

To me, a cloud is a distributed system of computing resources where the resources can be dynamically allocated with an API. A hosted application should be able to increase or decrease the available processors, memory, and disk without human intervention. Human oversight should be implemented at points where it makes sense for business and security, rather than at points dictated by the limitations of technology. This means a cloud should do be able to do significant automated management of DNS, networking, and provisioning of fundamental operating system details. The line between any classic distributed system or cluster and a 'cloud' is blurry, but generally speaking a cloud's API should be internet-compatible and capable of using commodity hardware to scale up with minimal (and preferably asynchronous) intervention from system administrators. As for 'The Cloud' -- currently I don't think there is 'The Cloud' the way there is 'The World Wide Web', but it's theoretically possible. Right now 'The Cloud' generally means 'A Public Cloud', which is a publicly available distributed system like the one I described above. A Virtual Private Hosting service is not a cloud, because allocation of resources typically involves a sales contract of some sort. But the service itself it might theoretically run on a cloud, and you can build a cloud out of VPSs.