Red Hat is a commercial Linux distribution and perhaps the largest Linux distro in enterprise segment.
Red Hat Enterprise Linux (RHEL) is the primary product of Red Hat, but there are many more open source projects that are maintained, supplied and supported by Red Hat:
Current version: RHEL 8.0 (released May 7th, 2019)
Current beta: RHEL 8.1
There is also a free distro called CentOS – it follows release schedule of Red Hat but comes without commercial support.