This is the name we use for AC systems that are filled with a black icky substance. As the name implies, it pretty much spells the end of your AC system. I believe this is the result of the rubber AC hoses coming apart internally. Honestly, I'm not sure what causes this, but whenever I see it, it pretty much means the end of the AC system for that vehicle. Everything will need to be replaced: the compressor, the hoses, the evaporator, the expansion valve, the condenser, and the receiver dryer. Once this stuff sets in, it never goes away. Complete replacement of all the AC components is the only thing I've seen cure this issue.