On a flight plan, POB means what is says "people on board"...
Meaning "crew + passengers"...
xxx
With my airline, we file TBN "to be notified" in that space, as we do not know the actual count, last minute changes of people boarding the plane. Then before we start engines, the senior flight attendant comes to inform the cockpit crew as to how many passengers have been counted. Then we inform the ground as to how many people are actually on board when requesting start clearance.
xxx
Happy contrails