Source : Free On-Line Dictionary of Computing

PPN
     
        Project-Programmer Number.
     
        A user-ID under {TOPS-10} and its various mutant progeny at
        {SAIL}, {BBN}, {CompuServe} and elsewhere.  Old-time hackers
        from the {PDP-10} era sometimes use this to refer to user IDs
        on other systems as well.
     
        [{Jargon File}]
     
        (1994-11-18)