Meaning of probable error

prob'able er'ror

Pronunciation: [key]
— Statistics. Statistics.
  1. a quantity formerly used as a measure of variability: equal to 0.6745 times the standard deviation. A normally distributed population has half of its elements within one probable error of the mean.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.