According to CentOS website, they use the source code from Red Hat, but I am not clear about what version of Red Hat source code is being used to build each version of CentOS.
Is there a numeric equivalent? For example, is CentOS 6.5 equivalent/based on Red Hat Enterprise Linux 6.5?
CentOS 6.5 is based on RHEL 6.5; prior to CentOS 7, CentOS versions exactly match RHEL versions. The pattern changed with CentOS 7, which uses something like a build number: CentOS 7 (1406) is based on RHEL 7.0, CentOS 7 (1503) is based on RHEL 7.1, etc. You'll find all the details on the CentOS wiki (look for the "Archived Versions" section).
Yes. CentOS uses the same major and minor release numbers as the RHEL version they are rebuilding.
