crack cocaine that is reprocessed (i.e. "cookback", "comeback") to remove impurities and creat a much more potent product at the loss of some weight and volume. Usually looks clearish white to yellow in color.
I used to smoke crack and everytime the dealers had butter we would come back all day long. Baking soda rock was a let-down. You can take about 1/3 the same amount of butter rock that you would take for a hit with some soda rock and feel higher off that one hit from the butter. Very potent crack cocaine that keeps the addicts comming back till it's gone.