Definition: The word "RHEL" stands for Red Hat Enterprise Linux. It's a popular operating system distribution that was developed by Red Hat. The term refers to version 4, which is the latest major version. Detailed definitions of the words vary depending on context: RHEL stands for Red Hat Enterprise Linux; H is for High Availability; R is for Relational Database; E is for Enhanced Security and for "Linux," meaning it's a modified Unix-like operating system that runs on top of Linux kernel, but it has its own hardware driver. So, in summary, "RHEL4" is the latest version of Red Hat Enterprise Linux, which stands for Red Hat Enterprise Linux 4. It's a modification of Linux, specifically developed by Red Hat for enhanced security and availability.