Expectation: Drop everything else and work continuously to resolve. An outage means that some piece of infrastructure that the community relies on is down. A P0 issue is more urgent than simply blocking the next release.
Example P0 issues:
Expectation: Continuous status updates. P1 bugs should not be unassigned. Most P1 bugs should block release.
Example P1 issues:
Expectation: Most tickets fall into this priority. These can be planned and executed by anyone who is interested. No special urgency is associated, but if no action is taken on a P2 ticket for a long time, it indicates it is actually just P3/nice-to-have.
Example P2 issues
Expectation: Nice-to-have improvements.
Example P3 issues
Expectation: Nice-to-have improvements that are also very small and easy. Usually it is quicker to just fix them than to file a bug, but the issue can be referenced by a pull request and shows up in release notes.
Example P4 issues