Crystals, specifically quartz crystals, are used in electronic circuits to create stable frequencies due to their high Q-factor (quality factor), which ensures low phase noise and high frequency stability. Quartz crystals operate on the piezoelectric effect, where mechanical stress produces an electrical charge and vice versa. Oscillators are circuits that produce a continuous, oscillating signal (sine wave, square wave, etc.) without an input signal. They generate clock signals for digital circuits and various other applications. Resonators are similar to crystals but typically have lower precision and stability. They are used in applications where cost or size is a more significant concern than frequency stability. Critical timing and frequency stability applications, such as communication systems, favor crystal oscillators, while cost-sensitive applications with less stringent requirements might use ceramic resonators or RC oscillators.