The Nyquist-Shannon sampling theorem

The Nyquist-Shannon sampling theorem states that if you want to perfectly reconstruct a continuous signal (like sound or an image), you must sample it at a rate at least twice its highest frequency component. This minimum rate is called the Nyquist rate. Sampling below this rate causes overlapping and distortion, called aliasing, which makes it impossible to accurately recover the original signal. Essentially, by taking enough measurements (samples), you can accurately recreate the original continuous signal without loss of information.