Wiktionary
n. The lowest rank of a commissioned officer in the RAF, equivalent to an Army ensign or coronet
Wikipedia
Pilot officer (Plt Off officially in the RAF; PLTOFF in the RAAF and RNZAF; formerly P/O in all services, and still often used in the RAF) is the lowest commissioned rank in the Royal Air Force and the air forces of many other Commonwealth countries. It ranks immediately below flying officer. It normally denotes an officer who has elected to join as a non-graduate direct entrant officer, as those with degrees usually serve only a week at the rank after graduation from the RAF College Cranwell. Some newly commissioned officers hold the lower grade of acting pilot officer.
It has a NATO ranking code of OF-1 and is equivalent to a second lieutenant in the British Army or the Royal Marines. The Royal Navy has no exactly equivalent rank, and a pilot officer is senior to a Royal Navy midshipman and junior to a Royal Navy sub-lieutenant. In the Australian Armed Forces, the rank of pilot officer is equivalent to acting sub lieutenant in the Royal Australian Navy.
The equivalent rank in the Women's Auxiliary Air Force (WAAF) was "assistant section officer".
Usage examples of "pilot officer".
Then as I was wandering down the street, I met a pilot officer I know.
The pilot officer in charge of drones jumped out, a stream of drone printout pictures crackling in the wind as he forced his way into the crowd, trying to tell them it had all come through on a drone overfly, trying to show people what had happened.
You didn't have a chance to get to know Pilot Officer Longo, but she was a nice woman and a good pilot.
He was made a Pilot officer in the Canadian Royal Air Force, and his combat flight training began.