sev-1, sev-2, sev-3. Well, that is for outages not really tasks. We don't assign priority values to tasks.
When I've seen priorities assigned to tasks, the practical end results always boiled down to: "interrupt current work to get it done", "do it in the 'next' batch of work", or "never do it". Even though there were often more than 3 levels defined (and that 3rd level doesn't really qualify as a priority anyway).