Red Hat Enterprise Linux. RHEL is a stable platform for businesses to run their apps on; they port upstream code fixes to their kernel and distribution and offer support for a price.

Now that Centos and RHEL will no longer be in lockstep, some people are looking for alternatives. The upgrade from 1 RHEL license to 16 is a way for Red Hat to try and retain small projects and let home labbers and evangelists legally replace Centos rather than switch.

Red Hat Enterprise Linux.

For context, CentOS was a popular Linux distro that tracked RHEL, being mostly identical except for not requiring a support package. Red Hat stopped supporting it, which put a lot of its users in a bind. This is intended to replace it.