The Kernel version is broken down into three parts:

1. Major Number
2. Minor Number
3. Revision Number

The Current Linux Kernel versions (June 2014) are:

• 3.14.5 (Stable – Maintained by Greg Kroah-Hartman)
• 3.15-rc8 (Development – Linus Torvalds)

The first number(3) is the major revision to the Linux Kernel. The second number(14) shows the minor revision. Development Kernels are odd and production kernels are even. Development kernels are not fully tested and can be unstable. Once a development Kernel is thoroughly tested and deemed stable is will be given an even number x.1.x → x.2.x or x.3.x → x.4.x
Since the Linux Kernel is constantly being improved and revised a revision number(5) is added when smaller changes are made.

How to tell which Linux Kernel you are running?
From your Linux Terminal type:

• uname -r
• cat /proc/version
• rpm -q kernel              (If you arte running Red Hat package manager)
• dmesg | grep Linux
• ls /boot                           (look for vmlinuz.x.x-x)

I hope this helps explain Linux Kernel versions.