In signal processing, what does 'aliasing' refer to?

Aliasing refers to the distortion that occurs when a signal is sampled at a rate that is insufficient to capture the changes in that signal accurately, specifically below the Nyquist rate. The Nyquist rate is defined as twice the highest frequency present in the signal being sampled. When signals are sampled below this rate, higher frequency components can be misrepresented as lower frequencies, leading to confusion and misinterpretation of the signal. This phenomenon is particularly critical in digital signal processing since it can severely degrade the quality of the reconstructed signal, resulting in a loss of information and fidelity. Understanding aliasing is crucial for designing systems and ensuring that samples are taken at an appropriate rate to preserve the integrity of the signal.