scum edit = starcraft ultimate map editor.
As mentioned before, in Warcraft 3 - you could edit a World. Hence, WorldEdit.
In Starcraft 2, you can create galaxies, hence Galaxy Editor.
I think the fact that it is called Starcraft 2 Editor - might just be something to do with it being Beta. Or, that's just what it was called at first.
It is (also as mentioned) Galaxy - the scripting language which makes Starcraft 2 do what it does.