• What is an Oscillator? 

An oscillator is a circuit that generates frequency with the help of a tuned circuit & that generated frequency is known as oscillating frequency.

• What is a Crystal Oscillator?

Similarly, a crystal oscillator is an electronic circuit or device which is used to generate a stable frequency with the help of a crystal instead of a tuned circuit. The crystal when vibrates, it acts like a resonator & as a result generates an oscillated frequency. The resonator circuit uses a crystal to generate the oscillation, led to the name as Crystal Oscillator. The symbol & circuit of a crystal oscillator is as shown below: