No real meaning... just a nasty sounding name to call someone when you're really pissed off at him. A word to be blurted out in anger, just like son of a bitch, cocksucker or asshole.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."