What do "N" and "P" in the codes of the proposals to the C++ standard mean?
Here is the list of GCC's standard support status. You can see the proposals are like "P0245R1" or "N4051", etc. (The "R", I assume, means "revision").
Meeting announcements, minutes, working drafts, editor’s reports, and official document submissions (CD, PDTS, etc.), and records of response must use N numbers.
All other documents should use P numbers.
Documents circulated as drafts should have D numbers (Dxxxx for N documents, and D0xxxRn for P documents). Only documents for publication should have the N or P numbers.