ACF (Autocorrelation Function)

The Autocorrelation Function (ACF) measures how closely a data point in a time series relates to previous points at different time lags. It helps identify repeating patterns, trends, or cycles within the data. For example, if daily sales tend to be higher every weekend, ACF will show a strong correlation at the lag corresponding to 7 days. Essentially, ACF reveals whether current values are influenced by past values and how this relationship changes over time, aiding in understanding and forecasting future behavior in time-dependent data.