[major].[minor].[patches].[revision]


[major] - Represents a real big change happened to the product, and then the major number will increase by 1.


[minor] - If there are some new features, improvements, enhancement or bugfixings have been made during developing a snapshot, this minor number will increase by 1.


[patches] - This number uses for indicating changes(patches or quick fixes in emergency) happened on the product whish is running in a wild.


[revision] - This number only uses for identifying a particular package of product which is in the stage of QA. The typical usecase is that if QA want to reopen a story, and kick back the package to developer, then after fixing the bug, deverloper have to repack the release candidate with a new revision increased by 1.