What is a PM?

From Barbelith

A "PM" is a "Private Message."

Think of it as board-only email, only without the ability to cc a bunch of people at once (as yet). If you're reading Bleeding Hands' insightful commentary on riots in Nigeria and you suddenly realize you might have gone to elementary school with hir, try not to rot the thread (See What is Thread Rot?) with your suspicion - instead, send a PM.