Forecast Error
Minimizing MAE produces forecasts of the median; minimizing RMSE produces forecasts of the mean. The metric is a modeling choice, not a scorecard.
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WMAPE (Weighted Mean Absolute Percentage Error)
WMAPE needs an explicit formula. Actual weights can reproduce WAPE, while business weights, aggregation, and zero handling change the result.
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sMAPE (Symmetric Mean Absolute Percentage Error)
The same ten-unit miss scores 0.09524 high and 0.10526 low. The name describes an intention, not the formula.
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WAPE (Weighted Absolute Percentage Error)
Two forecasts with identical 8% WAPE: one misses the big item by 11.4%, the other forecasts a small item at a fifth of its demand.
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Mean Absolute Percentage Error (MAPE)
Error as a percentage of the actual, averaged. Comparable across series, but it breaks at zero, explodes near it, needs a real zero, and rewards low forecasts.