semarket versioning (semantic versioning when marketing is in charge of the major version number).
the major number goes up, or down, when introducing major new features, whether or not they break backward compatibility. or other big changes like rebranding the company.
the minor number goes up when a backward incompatible change happens, and when a new feature is added that only the developers cared about.
the patch number goes up for bugfixes and/or backward compatible changes.