makes unrelated software on the system (or the whole system) break, or causes serious data loss, or introduces a security hole on systems where you install the package

the package has an issue with licensing (non-free), privacy, or security, or (in the package maintainer’s or release manager’s opinion) makes the package unsuitable for release

a bug which has a major effect on the usability of a package, without rendering it completely unusable to everyone

the default severity value, applicable to most bugs

a problem which doesn’t affect the package’s usefulness, and is presumably trivial to fix

for any feature request, and also for any bugs that are very difficult to fix due to major design considerations