Kernel Version Numbering scheme

Linux uses a Major Version, Minor Version and a Release Number to describe the kernel.

If a particular number is X.Y.Z then X is the Major Version, Y is the Minor Version and Z is the Release.

For example, Linux-2.4.20  describes it as Major Version 2, Minor Version 4, and Release 20.

All Odd Numbered Minor Versions are development versions such as 2.3, 2.5 etc.

whereas all Even numbered Minor Versions are stable, production versions such as 2.4, 2.6 etc.