An oscillator is an electronic circuit or device that produces a repetitive, oscillating signal, typically in the form of a sine wave, square wave, or triangular wave. It converts direct current (DC) from a power source into an alternating current (AC) signal, which is used in various applications such as clocks, radios, and signal processing. Oscillators are essential in generating clock signals for digital circuits and in communication systems for modulating and demodulating signals.