A DCC controller is a device used in model railroading to manage and control digital commands sent to locomotives and accessories. DCC stands for Digital Command Control, which allows multiple trains to operate independently on the same track without the need for complex wiring. The controller sends digital signals that communicate with equipped trains, enabling features like speed control, direction changes, and sound effects. This technology enhances the realism of model railroads, allowing hobbyists to create intricate layouts with ease and flexibility.