Exactly.
VDS = Dual Core Server 1 core to each VPS on the server. (Very basic example). No redundancy.
VPS = Resources are shared. OpenVZ Memory, Disk, and CPU can be oversold. KVM/XEN CPU is typically oversold (not really such a big deal as long as the node is managed right). KVM/XEN can oversell disk if they use a thin provision type image. Limited redundancy options.
Cloud = This can go any number of ways however this should have true redundancy and depending on the setup the ability to scale resources on demand. We use OnApp for these features with KVM as the underlying VPS technology. My newest OnApp 3.1 cluster will have some very useful setups for anyone looking for redundancy in many different formats.
