WordNet (r) 3.0 (2006):

Nyquist frequency
    n 1: (telecommunication) twice the maximum frequency occurring
         in the transmitted signal

The Free On-line Dictionary of Computing (30 December 2018):

Nyquist frequency

    The highest frequency that can be represented in a
   digital signal of a specified sampling frequency.  It is
   equal to one-half of the sampling rate.

   See Nyquist Theorem.

   (2001-06-06)