vCloud is a cloud computing initiative from VMware which will allow customers to migrate work on demand from their "internal cloud" of cooperating VMware hypervisors to a remote cloud of VMware hypervisors. The goal of the initiative is to provide the power of cloud computing with the flexibility allowed by virtualization.
vCloud supports so called hybrid cloud solutions where a customer runs (part of) his cloud on his own dedicated hardware with the ability to move VM's running on the private infrastructure to the public cloud. This will give the user even extra flexibility: when external events (or seasonal effects) lead to a large extra increase in required computing (and/or storage) demand, the cloud manager can start using cloud services from his external provider.
VMware vSphere: Install, Configure, Manage [V4.1 or V5.0]