Autocorrelation — correlation between a series and a lagged version of itself.
Backtesting — simulating historical forecasts using only information available before each forecast origin.
Baseline — a simple reference forecast that an advanced model should improve upon.
Drift forecast — extrapolation of the average change observed between the first and last training values.
Expanding window — evaluation where the training set grows as the forecast origin moves forward.
Forecast horizon — number of future periods predicted.
Lag — a past observation used to explain or predict a later value.
Leakage — use of information during training that would not be available at prediction time.
MAE — mean absolute error; average absolute distance between actual and predicted values.
RMSE — root mean squared error; penalizes larger errors more strongly than MAE.
Seasonal naive — forecast that repeats the most recent observed seasonal cycle.
Seasonal period — number of observations in one repeating cycle, such as 12 for monthly annual seasonality.
sMAPE — symmetric mean absolute percentage error; a scale-relative percentage-style metric.
Temporal holdout — final chronological portion of a series reserved for evaluation.
Walk-forward validation — repeated forecasting from successive historical origins while preserving temporal order.