* any bug that has a high user impact
* String changes may not be approved after the string freeze dealine
* a low risk Polish polish change : Visual polish - colors, sizes, icons, alignment, etc
* functional-polish: Example, Notification tray displaying that your microphone is active, but onclick does not do do anything. Ideally it should take to to microphone settings if I wanted to play with it..It's not really a bug, but it could be better. And it requires code changes, not just visual work.
* papercuts: It's for issues found during dogfooding/testing that are visually or functionally annoying or otherwise sub-par, but not enough to block the release