geometric mean
    n 1: the mean of n numbers expressed as the n-th root of their
         product

geometric mean

    The Nth root of the product of N numbers.

   If each number in a list of numbers was replaced with their
   geometric mean, then multiplying them all together would still
   give the same result.  The geometric mean thus gives an
   average "factor" in a context where numbers are multiplied
   together, e.g. compound interest.

   <Wolfram>.

   (2007-03-16)