Abbreviation for Variable Frequency Oscillator: a somewhat generic term that can refer to all oscillators with variable frequency abilities. While the term can be used generically it tends to show up most commonly in radio transmission parlance. Radio frequency VFO’s are often used superheterodyne AM and FM tuners to produce waveforms that combine with the transmitted carrier as part of the reception process (see WFTD Heterodyne for more background). In music synthesis VFO’s are common, however, they tend to be referred to by more specific names that denote the method for changing the frequency, such as VCO (Voltage Controlled Oscillator) or DCO (Digitally Controlled Oscillator).