Original: Control of the aircraft is normally shared equally between the first officer and the captain, with one pilot normally designated the "Pilot Flying" (PF) and the other the "Pilot Not Flying" (PNF), or "Pilot Monitoring" (PM), for each flight.
Simplified: Control of the aircraft is normally shared equally between the first officer and the captain, with one pilot normally designated the "Pilot Flying" (PF) and the other the "Pilot Not Flying" (PNF) for each flight.