A Phase-Locked Loop (PLL) is an electronic circuit used to synchronize an output signal's phase with a reference signal. It works by comparing the phase of the two signals and adjusting the output to minimize any phase difference. This makes PLLs essential in applications like radio, telecommunications, and clock generation. PLLs consist of three main components: a phase detector, a low-pass filter, and a voltage-controlled oscillator (VCO). The phase detector identifies the phase difference, the low-pass filter smooths the output, and the VCO generates a signal that matches the desired frequency. Together, these components enable precise control of frequency and phase.