I get the sense that hack and slash refers to a gameplay style prevelent in God of War and Dynasty Warriors. The sense of button mashing like crazy or using repetitious combos (repetitive gameplay is another discussion all together) with literally minimal consequence. There's no sense of realism, because you can batter away at enemies and soak up damage but keep pounding till they die.
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"Should I slice off your tongue or break your countless bones? Either way, I get paid; you'll bleed to death and die alone." - Blood Money