Building on @John Siu's answer the terminology is confusing if you're not familiar with the Red Hat technologies.
- RHEL - Enterprise Linux (commercial version of Red Hat's OS)
- CentOS - Community version of RHEL (binary compatible with RHEL)
- Fedora - Bleeding edge OS built by the Fedora Project (Red Hat sponsored community proj.)
- RPM - RPM Package Manager (formerly Red Hat Package Manager)
RPM isn't a Red Hat only technology, OpenSUSE uses
RPMs as well and these are not necessarily compatible with
RPMs built for one of the 3 Red Hat based distros (RHEL, CentOS, or Fedora).
New technology usually shows up first in Fedora where it is worked out. Fedora distros usually have a shelf life of 13 months. At any time 2 releases are being actively supported, after which updating for it is dropped.
Once technologies have been proven out in Fedora they'll eventually show up in a release of RHEL. RHEL's shelf life is 10 years of production followed by 3 years of extended coverage. See here for full details.
CentOS is a community project that is now sponsored by Red Hat but which is operated separately from RHEL. CentOS provides the same identical packages as RHEL with the RHEL branding stripped out and/or replaced with CentOS logos and branding. CentOS is sponsored by several customers that have very large numbers of computers but don't want to have to pay for a subscription of RHEL for each box. The CentOS project doesn't offer any support other than staying in lock step with updates as they come out for RHEL.
There are a lot of other distros that make use of
RPMs for package management. Some derive from Red Hat distros while other only make use of
RPM the technology but are not compatible with Red Hat distros in any way, such as openSUSE.