1. the mean of n numbers expressed as the n-th root of their product;

WordNet (r) 3.0 (2006):

geometric mean n 1: the mean of n numbers expressed as the n-th root of their productThe Free On-line Dictionary of Computing (30 December 2018):

geometric meanThe 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 (http://mathworld.wolfram.com/GeometricMean.html). (2007-03-16)