Usually it's a weapon with multiple possible attacks, keyed to some kind of randomizer - the traditional form is dice. I think the theory's that it avoids overloading the quantum generator that creates the effects, but there's a certain kind of glory-hound who appreciates the dramatics of leaving the details of a fight up to chance.

Granted, the dice mostly fell out of favor centuries ago, partly because they're so unreliable. I've only ever actually encountered one person who wielded them, and I have no idea how she gets them to work as well as she does.