Today, I found out that I have SSed more levels in Dustforce than one of the developers of the game. That's interesting food for thought.
What does "SS" mean here? Super Special?
When you beat a level, you are graded on Completion and Finesse.
Completion = how much of the dust you cleared in the level
Finesse = how well you kept your combo. You lose combo if you get hit, die, or go too long without collecting dust
Ranks are from D to S for both. An SS means you cleared all the dust while keeping a full combo. On the later levels this gets really, really hard.
The dev has SSed all but 7 levels, I've SSed all but 1.