ZBB or Zero Bug Bounce is a defect management technique originating from Microsoft that represents the moment (would prefer to call it a milestone) in time when the developers has managed to fix (or triaged) all the bugs reported by the QA team. The bounce refers to the fact the QA team might (and surely will) find bugs again increasing the count of bugs. The rate of discovery of bugs gradually tend to decrease as the application gets ready for release.
So what is the significance of ZBB ? It surely doesn’t mean the application is ready for release as there is a bounce expected. But the ripple or the bounce, gives the team a good indication of how stable the application is and how closer are we nearer to a release. Surely, that is an useful indication which the development team and Managers would like.