Fluctuation

Fluctuation, random fluctuations - random, unpredictable deviations from the mean value of a random variable (e.g. a physical quantity) subject to stochastic changes over time and showing no trend.

Fluctuations are present in all stochastic processes, in physics, both in classical and quantum systems, also in econometrics, biology, etc. They are inherently associated with statistical and prognostic errors. They appear as a component of the time series (trend + seasonality + random fluctuations).