DCC stands for Digital Command Control.
DCC is a control system for model railways.
DCC lets you control mutliple trains on the same track(s) with the bare minimum of wiring.
DCC lets you control these trains independently of each other - they can be travelling at different speeds and in different directions.
DCC lets you control these trains all from one controller, or...
DCC lets you add more controllers without the need for any switches and their associated wiring.
DCC lets you control not just the motion of the locos, but things like lights and sound too.