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."