Wookieepedia defines a superweapon as "A superweapon was a weapon capable of destroying entire planets or systems." I think that is a good definition. I think the introduction on this page provides a good way of looking at them based on real-life. Then there is Wiki's superweapon page. SO, the real question, SOCL, is "Do you want to talk about real, fictional, or both kinds of superweapons?" A possible follow-up question is "If fictional, SW only or do you want to discuss other series'?"