control voltage (vc systems)   

A control voltage is a voltage in the range of 0 - 10 volts (usually) which is used to control various modules in an analogue system.
it may be alternating or direct current, though most often the latter. conventionally, analogue synthesizers used a 1 volt/octave standard.  This meant that a change of 2 volts to a voltage control oscillator would shift the perceived pitch by two octaves.