From Glossary of Meteorology
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  1. The introduction of error in the Fourier analysis of a discrete sampling from continuous data, by which frequencies too high to be analyzed with the discrete sampling interval erroneously contribute to the amplitude of the lower frequencies.

    Aliasing can be avoided by filtering out the high frequencies (using slower-response instruments or analog electronic circuits) before sampling or digitizing.
    See also Nyquist frequency.

  2. In radar, sodar, and lidar, the folding of target returns from outside the normal unambiguous range interval (range folding) into the normal range interval, or the folding of radial velocity measurements outside the unambiguous velocity interval (velocity folding) into the normal velocity interval.