P-Rank

Similar to S-Rank, it is used to describe something so supreme it does not fit into traditional ranking system.
It's like 50/10, if 11/10 is S-Rank.

Originally from the Video Game "Ultrakill" by New Blood. It has a Devil May Cry-like ranking system for level completion, in which P-Rank is the best, and only achieved by getting the highest rank in time, kills, and score.
The 'P' most likely stands for 'Perfect'.

It's so hard to get P-Rank, I can only ever get to S!