VMware vCloud Director (vCD)

VMware vCloud Director is a new abstraction layer.VMware vCloud Director does not only abstracts and pools resources it also adds a self service portal.it is more or less bolted on top of vCenter/ESX(i).
As stated before, vCD abstracts resources which are managed by vCenter. Below each of the resource types I have mentioned what it links to on a vSphere layer so that it makes a bit more sense:
Compute
- clusters and resource pools
Network
- dvSwitches and/or portgroups
Storage
- VMFS datastores and NFS shares
As a vCD Administrator you can use the vCD portal to carve up these resources as required and assign these to a customer or department, often referred to in vCD as an “Organization”.
In order to carve up these resources a container will need to be created and this is what we call a Virtual Datacenter. There are two different types of Virtual Datacenter’s:

Provider Virtual Datacenter (Provider vDC)
A Provider Virtual Datacenter is the foundation for your Compute Resources. When creating a Provider Virtual Datacenter you will need to select a resource pool, however this can also be the root resource pool aka your vSphere cluster. At the same time you will need to associate a set of datastores with the Provider vDC, generally speaking this will be all LUNs masked to your cluster. Some describes the Provider vDC as the object where you specify the SLA and I guess that explains the concept a bit more.

Organization Virtual Datacenter (Org vDC)
After you have created a Provider vDC you can create an Org vDC and tie that Org vDC to a vCD Organization. Please note that an Organization can have multiple Org vDCs associated to it.

To summarize, vCD offers a self service portal. This portal enables you to provision resources to a tenant and enables the tenant to consume these resources by creating vApps. vApps are a container for one or multiple virtual machines and can contain isolated networks.