Very commonly used acronyms in business/SWE contexts.

The lower the number the higher the priority, e.g. if production is broken someone might say "This is p -1" (higher than your highest priority).

P0 is "do this immediately", P1 is very important, P2/P3 are like "nice to haves." P100 would mean something like "we will never do this"

priority 1,2 etc, more like severity of the cases

It’s a very common abbreviation; i had no issue understanding GPs post tbh