Officially, I believe that PNA has no meaning it is just the family name for a series of VNAs. We like to say it stands for "Performance Network Analyzer" or "Precision Network Analyzer".
Seriously, it is NOT a three letter acronym, it is the name of one of our network analyzer series. For reasons that I don't understand, we are NOT to refer to it as a Performance Network Analyzer shorted to PNA, as there is some (legal?) reason why we cannot trade mark or something a TLA but we can a three letter name.
So it could also (and has been) referred to as a Precision Network Analyzer, or even a Profound Network Analyzer.
Maybe, someday, it will be known as the WBNA (which is currently the 8753). I see OJ beat me to it
We like to say it stands for "Performance Network Analyzer" or "Precision Network Analyzer".