+Acf, or Autocorrelation Function, quantifies the similarity between observations of a [Time Series](/wiki/time-series) as a function of the time lag between them. It reveals hidden patterns, such as periodicity, by measuring how much a signal correlates with a delayed version of itself, a key tool in [Signal Processing](/wiki/signal-processing).
+## See also
+- [Cross-correlation](/wiki/cross-correlation)
+- [Partial Autocorrelation](/wiki/partial-autocorrelation)
+- [Stationarity](/wiki/stationarity)