DC stands for Direct Current (http://en.wikipedia.org/wiki/Direct_current). This is just using DC electricity through the rails to a DC motor in the locomotive.
DCC stands for Digital Command Control (http://en.wikipedia.org/wiki/Digital_Command_Control), it sends messages over AC (alternating current) power to microchips in the locomotive that then controls the locomotives.
DCC stands for Digital Command Control (http://en.wikipedia.org/wiki/Digital_Command_Control), it sends messages over AC (alternating current) power to microchips in the locomotive that then controls the locomotives.