: This refers to the correlation of a signal with a delayed version of itself. It is a critical concept because current values often depend on past values.
: Ups and downs that are not of a fixed period, often related to business cycles. Introduction to Time Series and Forecasting
: A stationary time series has statistical properties (like mean and variance) that do not change over time, which is a common requirement for many forecasting models. : This refers to the correlation of a
: Random noise or "leftover" variation after accounting for the other components. Common Forecasting Methods higher sales every December).
: Periodic fluctuations that occur at fixed intervals (e.g., higher sales every December).