When Red Hat started out, there was no such thing as an enterprise Linux distribution. A Linux distribution was simply that – a distribution of software collected together. Red Hat helped to change that model over the years and it’s most significant contribution was arguably the creation of Red Hat Enterprise Linux, 10 years ago.
Instead of the (relatively) rapid release rate of Red Hat Linux, Red Hat Enterprise Linux (RHEL) was intended to provide enterprise stability and longer release cycles of 18-24 months. Red Hat Linux back then iterated as many as three times a year and that was seen as a barrier to commercial adoption. RHEL soon after its creation became so popular that it killed Red Hat Linux as a standalone business.