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

McCulloch-Pitts neuron

    The basic building block of
   artificial neural networks.  It receives one or more inputs
   and produces one or more identical outputs, each of which is a
   simple non-linear function of the sum of the inputs to the
   neuron.  The non-linear function is typically a threshhold or
   step function which is usually smoothed (i.e. a sigmoid) to
   facilitate learning.

   (1997-10-11)