X-residuals

Contain the variance in the predictors not explained by the PLS model. Observations with relatively large x-residuals are outliers in the x-space, indicating that they are not well explained by the model.

The x-residuals are the differences between the actual predictor values and the y-calculated values and are on the same scale as the original predictors. The x-residual matrix, similar to the original x-matrix, is an n x p matrix, where n = number of observations and p = number of predictors.