There are many possible meanings for the initials, PFC, depending on the context in which they are used.
In the US Army, PFC means "Private First Class". PFC is the third lowest enlisted rank in the US Army, above two forms of the rank of Private and below Corporal.
In the US Marine Corps, the rank of PFC is the second lowest rank, above that of Private and below that of Lance Corporal.
An Army PFC has rank equivalent to a Marine Lance Corporal.
Among a large number of possibilities, PFC can also mean:
corporal - like Radar O'Riley and Max Clinger of Mash fame.
It is not a military custom it's a military command, 'stand at ease' means to relax from the 'stand to attention' command.
Kapaz PFC was created in 1959.
Sumgayit PFC was created in 2010.
AZAL PFC was created in 1996.
Simurq PFC was created in 2005.
PFC Oleksandria was created in 1991.
Pakistani Fried chicken, instead of fried chicken, because in the UK most fried chicken shops are run by pakistanis.
Depending on how it's used, it could stand for "Military Specification", meaning the ability to withstand shock, dust, or harsh environments.
Military Specification
MPO stand for Military Police Officers.
P=Protestant Pvt. would be Private Pfc. would be Private, 1st Class