Internal vs. external
With an internal cloud, no resources are shared. You have to build your own cloud. You pay for everything up front. For example, you buy the all of the hardware and all of the networking structure to built up your own cloud. Generally, there are no ongoing costs besides the cost for power and to maintain cooling in the data center.
With an external cloud, you share resources with a public cloud. The underlying infrastructure is purchased and owned by a third party cloud provider. Cost may be metered, where you are charged by usage, or the cost may be an up front cost.
