What does all the .222 or .688 mean

I have installed a leaked os on my phone before but I do not know the specifics. I do not know what all the numbers tied to the links mean. If a leak is .222 at the end, what is the difference between .355 or .688? Does the higher the number mean something? Just curious.
Thanks

Higher # in progression, but doesn't mean better.

Posted from my CrackBerry at wapforums.crackberry.com

The different numbers are RIM's (or any software developer really) way of distinguishing between different versions of a given bit of software... 5.0.0.591 would be an earlier version of an OS than 5.0.0.643 leak or 5.0.0.732 official for Tour, for example. This works the same for all software. As was mentioned, later builds aren't necessarily better. Sometimes they fix one thing but something else is broken, etc.

When discussing BB OS versions, the one everyone discusses is "app version".

Thanks a lot for the info guys. It was a lot of help.