A way of rolling dice in certain role-playing games; The old West End Games Star Wars RPG comes to mind, as does Legend of the Five Rings.

The idea is, if you roll a 6 on a D6, or a 10 (0) on a D10, whatever the maximum roll on a given die, you roll it again and add the two rolls. If you're extraordinarily lucky and roll a 10 (or whatever) twice, you get to roll again, and so on. Star Wars calls this the "wild die", and only one die is open-ended in this manner. In L5R, all dice have the potential to "explode", as they put it, and generate very large numbers.

I like this idea; it lends drama to a game knowing even if you have a lousy roll for something, the possibility exists of just randomly kicking arse because you got to be a lucky bastard once. On the other hand, usually you get really lucky for a really stupid things, and never when you need the luck. Oh well. Life is a hollow lie, and all that.