Red Hat Linux 6.2E was the first "enterprise" release they made. Basically just standard RHL 6.2 but with long-term support. This release can be retroactively thought of as "RHEL 1"; The proper distribution that debuted as Red Hat Enterprise Linux 2 was based on Red Hat Linux 9, with the similar promise of long-term support. Future RHEL releases are carved out of Fedora releases, the spiritual successor to RHL.