the.com/standard deviation

means A single number that measures how spread out a set of values is around their average — small means the data huddles close, large means it's scattered wide.

from The term comes from statistics in the late 1800s, coined by the English mathematician Karl Pearson, who was building out the vocabulary of modern statistics (he also gave us 'variance' and popularized the correlation coefficient). 'Deviation' simply means a departure from a fixed point — here, the mean — drawn from Latin 'deviare,' to turn aside from the way. 'Standard' marks it as the agreed, normalized measure of that wandering, so the word is less a metaphor and more a label: the standard way to measure how far things stray.