The Nyquist-Shannon sampling theorem is a fundamental principle in signal processing that defines how to accurately sample a continuous signal. It states that to reconstruct a signal without losing information, it must be sampled at least twice the highest frequency present in the signal. This minimum rate is known as the Nyquist rate. If a signal is sampled below this rate, it can lead to aliasing, where different signals become indistinguishable when sampled. This theorem is crucial in various applications, including digital audio, video processing, and telecommunications, ensuring that signals can be accurately captured and reproduced.