What is aliasing and how is it prevented in data acquisition systems?

Aliasing occurs when sampling rate is less than twice the highest signal frequency (Nyquist criterion), causing high-frequency signals to appear as false low-frequency components. Prevention: anti-aliasing filter (low-pass filter before ADC with cutoff at less than half sampling rate), increased sampling rate, or oversampling with digital filtering. Anti-aliasing filter must have sufficient roll-off to attenuate frequencies above Nyquist. Rule of thumb: sample at 5-10x highest frequency of interest. Aliased signals cannot be recovered - prevention is essential.