We recently published an extensive article on "the bumpy road to the private cloud," which provided a huge amount of information on what a private cloud is, and how to get there (it isn't easy). I recommend taking a look! Here's a supplemental -- and much shorter -- way to look at the private cloud, courtesy of the folks at the Corporate Executive Board.
The five characteristics of a private cloud:
1. Scalable: High levels of utilization (e.g., through virtualization, and the size and maturity of data centers)
2. Accessible: IT customers can self-provision
3. Elastic: Appearance of infinite capacity on demand
4. Shared: Workloads are multiplexed, capacity is pooled
5. Metered consumption: Ability to pay for use with no commitment
Source: Corporate Executive Board's Infrastructure Executive Council, Arlington, Va.
This story, "The Five Characteristics of a Private Cloud" was originally published by Computerworld.