Submariner slang for a
slacker,
layabout,
malingerer,
goldbricker or
freeloader.
Based on the notion that because submarines are closed systems, each individual on board represents a definite load on the ventilation systems and CO2 scrubbers, and so if a crewman is taking it easy, he is stealing from the rest of the crew.
One of the harshest insults used on board.