Damn good question. To me it meant that the device was based on some form of believable science for the genre (no laser pistols in modern detective fiction or 9mils in fantasy etc.... This doesn't mean that you can't have one with GM permission - remember the Warlord - just that you got no bonus), had mass (more damage potential resulting in larger mass and size - more dificult to conceal for one), took time to draw and aim and was hampered by poor weather/environmental (won't shoot when wet etc...) conditions. General inconveniences caused by the "real world" nature of the weapon.