This file specifies the version of the Linux kernel, the version of gcc used to compile the kernel, and the time of kernel compilation. It also contains the kernel compiler's user name (in parentheses).

Linux version 2.6.8-1.523 ([email protected]) (gcc version 3.4.1 20040714 \  (Red Hat Enterprise Linux 3.4.1-7)) #1 Mon Aug 16 13:27:03 EDT 2004

This information is used for a variety of purposes, including the version data presented when a user logs in.