Creativity is the ability to invent new and interesting methods of dealing with badfic. There are other meanings, but this is possibly the most applicable to the PPC.
More generally, creativity is the aptitude for being creative. People with this aptitude like to imagine new, original ideas and put them into practice, either through writing, art, interpretive dance, mathematical formulae, underwater basket-weaving, or really anything at all that takes their fancy. There is no field in which creativity is not an asset.
Agents are often very creative, especially when explosives and Bad Ideas are involved.
Mary Sues, on the other hand, tend not to be very creative, which is why most Suefic is so very much alike.