Control Voltage, also called CV, and 0–10V Control, is one of the earliest and simplest electronic lighting control signaling systems.  The control signal is a DC voltage that varies between zero and ten volts. The controlled lighting should scale its output so that at 10V, the controlled light should be at 100% of its potential output, and at 0 V it should at 0% output (i.e., off).  Wikipedia provide more information.