That slimy, often smelly, nastiness that you find in the oddest of places. ie- the drain of your shower, in your hair after jumping into a stagnant pond, off your truck after a day of mudding in a cow pasture, in the bottom of the fridge catch pan, under the sink that's been leaking for years without your knowledge, on the bottom of your work boot, in your hair or on your clothes after a long drunken night of partying, in your car cup holder.
It's hard to clean and/or get rid of. It's often of very thick consistancy and can stain anything it touches. Beware of Scwoogie Goo as no one can accurately describe it's contents and it can be very harmful to your health if swallowed or otherwise ingested.