Centos stands for Community ENTerprise Operating System. It is a Linux distribution based on the Source RPM’s of Redhat Enterprise. It has the same functionality as Redhat enterprise, but does not include some of the Redhat Specific support tools.
The Centos Team work hard making this distro comply with Redhat’s redistribution policy by re-branding and removing Redhat tools. Updates are also provided using an update mechanism similar to Redhat network. I actually find the Centos update network better due to it’s more intelligent use of local mirrors.
Centos does not currently have an official commercial support structure, however this is why it came into existence. Some solutions do not actually need ongoing paid subscription. If you do, use Redhat Enterprise.
This does not mean that Centos does not have support. It is supported by a number of people ( such as myself, and a number of resources on the internet
If you are looking for a stable Linux platform to place the a growing number of Redhat certified applications, consider centos.