A special case of an estimate of the variability of data is the estimated standard deviation. For example, if we know that data follows the Normal distribution (say people's heights), we might work out the standard deviation of the population for a sample, and then use this as an estimate of the true standard deviation.
Also used in hcistats2e: Chap. 8: page 93
Used in glossary entries: estimate of the variability, estimated standard deviation, Normal distribution, standard deviation (s.d., σ), standard deviation of the population