: Random, unpredictable variations that cannot be explained by the other three factors. The "Forecasting" Edge Time Series Analysis Forecasting And Control

: Long-term fluctuations that aren't tied to a fixed schedule, often mirroring economic or business cycles.

: Regular, repeating fluctuations linked to the calendar, such as increased retail sales during December.

: The long-term direction of the data (e.g., a steady rise in e-commerce sales over a decade).