An oscillator is an electronic circuit that creates a repeating signal. The signal might be a sine wave, square wave, pulse, clock, tone, or radio-frequency signal depending on the design.
Why oscillators are used
Oscillators provide timing and rhythm for circuits. They are used in clocks, radios, microcontrollers, signal generators, audio circuits, wireless systems, and switching power supplies.
Oscillator versus crystal oscillator
A crystal oscillator uses a quartz crystal to create a very stable frequency. Other oscillator circuits may use resistors, capacitors, inductors, or active components.
If a circuit needs a steady repeating beat, an oscillator is often the source.