usually a 2 or 3 man position in front of the main defensive position opcon ( ed ) when one unit is placed under another unit not normally in their chain of command pa physicians ' assistant pax passenger terminal at a military airbase pisser latrine pkm russian made medium machine gun pl platoon leader ( usually a newly commissioned officer ) platoon 4 to 5 squads pog ( or pogue ) see fobbit , usually anyone not in a combat mos psd personal security detachment psg platoon sergeant ( usually a senior nco ) pt physical training ptsd post-traumatic stress disorder px post exchange , the base shopping center r & r rest & relaxation , either two weeks home in the states or a three day pass in qatar rear detachment parts of a unit that remain behind at home base for administrative services .