Term of affection for that tired, filthy, thirsty, hungry, footsore, ripped-trouser, camouflage-painted, lean, mean, son a b*itch who has kept the wolf away from the door for over two hundred years.

US Marines - (03--)
US Army - (11-)

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 :-)

Marines or other military serviceman who serve in the frontlines of war

Grunt is an acronym used during WW2 for troops who had no formal training, or skills. G-general, R-replacement, UNT-untrained,...GRUNT, as they had no special training, they were given rifles and sent to the front.

The warriors on the battle field, the men in the shit. The ground re-enforcement unit for any armed forces.

A guttural noise made for several different circumstances: happy, sad, yes, no, oh yes, oh god yes, during sex, taking a shit

Those annoying little fucks in Halo.