Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In statistics, the fraction of variance unexplained (or FVU) in the context of a regression task is the amount of variance of the regressand Y which cannot be explained, i.e., which is not correctly predicted, by the explanatory variable X. For a more general definition of explained/unexplained variation/randomness/variance, see the article explained variation.