probability density function n (Statistics) statistics a function representing the relative distribution of frequency of a continuous random variable from which parameters such as its mean and variance can be derived and having the property that its integral from a to b is the probability that the variable lies in this interval. Its graph is the limiting case of a histogram as the amount of data increases and the class intervals decrease in size. Also called: density function Compare cumulative distribution function, frequency distribution Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014probabil?ity den`sity func`tion n. 1. a function of a continuous variable whose integral over a region gives the probability that a random variable falls within the region. 2. a function of a discrete variable whose sum over a discrete set gives the probability of occurrence of a specified value. [1935?40] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.