The term "cloud" is thrown around all the time and means different things to different people. At the basis of the term once you are virtualizing anything you are using the cloud. If it is within your facility then you have a private cloud. If you have been using GMAIL/HOTMAIL/YAHOO?etc... for email than you've been using the cloud for years.
VCD basically allows you to have Infrastructure as a Service. The VCD administrator carves up resources and gives them to the end users. Those users can then provision how they want to within the boundaries provided. This allows users to provision on demand (within limits) and administrators to control the hardware layer. Typically VCD is not used for desktop systems except for testing environments.