CV (Control Voltage) in the world of analog modular synthesizers is typically any signal within the bounds of the systems power supplies (e.g. -12 to +12 Volts for Eurorack).
CV can typically can also be Audio (AC), Gates (DC), Triggers (Short DC pulses) or modulations (slow changing voltages) — or any weird mixture of those.
The difference to "normal" audio inputs is typically just that audio inputs limit the bandwidth for the low frequencies roughly at the audible range, while CV inputs can also accept DC).
Another thing: there are certain interface standards like e.g. oscillators accepting 1V/Octave inputs.
That means most Eurorack modules that produce tones have an calibrated input into which you can e.g. route precisely 1V to make the tone go up an octave, -4V down four octaves etc. If you route in 1/12V it goes up an semitone. If your signal is in between you do microtonal changes, vibrato, pitch bend and similar things.
https://en.wikipedia.org/wiki/CV/gate
Or something else altogether?