Imagine racks of servers, humming along in a data center. Together, these servers become a massive pool of resources. Divide this "pool" into multiple virtual servers, and you create a "cloud."
For the utmost security, create a private cloud on dedicated hardware. But always remember to put appropriate security measures in place, no matter which cloud you choose.
Since virtual servers aren't physical, they are super flexible, giving you what you need at the moment. Spin up a server in minutes, and take it down just as easily.
You'll get the greatest cost savings in the public cloud, where your virtual servers run on physical servers that you share with other customers.
In the open cloud, you can easily move your cloud around—without being locked into one provider or a closed, proprietary technology.
A hybrid cloud gives you the benefits of both public and private clouds. For example, you can put public-facing components in a public cloud, while storing customer-sensitive data in a private cloud.