Hi Wiix
PN - short for Peripheral Neuropathy - you're not ignorant - it's just there are so many people here with it that it has become common to shorten it.
If you find yourself wondering again what an abbreviation means there's even a thread that lists them - it doesn't cover everything so by all means keep asking.
Here's the thread:
http://neurotalk.psychcentral.com/showthread.php?t=255
It can also be found by going to the forum start list and read "Community Guidelines" - there's a link to it there.