(1) (Voltage Controlled Oscillator) An oscillator that can be tuned over a wide range of frequencies by applying a voltage (tuning voltage) to it. Used in many applications such as radio tuners, VCOs are less costly than crystal oscillators, but not as stable. Contrast with crystal oscillator.

(2) (Voice Carry Over) A telephone that allows deaf people to read incoming messages from a relay service, but lets them use their voice to respond.