The term "grunt" is used in the military as a general term for someone who's MOS (Military Occupational Specialty) is "Infantry". In the
Marine Corps all MOS' preceeded by the number "
03" are Infantry. About as "grunt" as you can get in the Corps is "0311 - Basic Rifleman".
The opposite of a "grunt" is a "pougue", which is a derogatory reference to pretty much anyone who isn't a grunt, but normally reserved for Marines who work in an
office or some other rear-echelon job as part of their regular duties ("In the rear with the
gear"). Call a pougue a "grunt" and they love it, but call a grunt a "pougue" and see what happens :-)
"If you ain't a grunt you ain't
SHIT"
"The grunts at Phase Line Echo report multiple hostiles, scattered
small-arms fire and are currently engaging."
"The fuckin' grunts always come to our E-Club and start
shit."