Has to be said we don't follow the definitions of the Linux Kernel numbering scheme so tightly, but we do follow the practice of odd numbering for development releases
In the numbers x.x.x
- This number is changed when really huge changes happen to phpBB such as what happened between 2.0 and 3.0
- This number is the number we increment when we start a totally new version, if this number is odd it indicates a development release, if it is even it indicates a stable (or soon to be) version.
- This is the revision of the previous two, so when we found bugs in 3.0.0 we upped it to 3.0.1 and we will continue to do so until 3.0 is no longer supported and there are bugs to fix.
Together the first two numbers indicate the version of the product, eg Windows 2000, Windows XP etc. and in our case phpBB 2.0 and phpBB 3.0. In the future there will be a phpBB 3.2, currently there is a phpBB 3.1 which is the code that will, in time, become phpBB 3.2.
Another thing to note, version numbers are not decimal numbers you don't go 3.0.9 -> 3.1.0 etc.