Can "fold" be used as a noun to describe groups in k-fold cross-validation? In a k-fold cross-validation, we divide the data into k groups. Are these groups called the "folds"? Can the word "fold" be used when I talk about these groups? Is it usual? Is the "fold" even a noun in this context in the statistical English?
If not, how do you call these k groups? Just "groups"?
PS: I am not a native speaker so I cannot judge it by "feeling"... I haven't found any dictionary definition of the noun "fold" that would be fitting. Anyway, I do not feel like asking this question other people than statisticians, since the English language used in statistics might be very different from the common English.

Yes, you can use fold as a noun when referring to the groups:

An alternative to LOOCV is k-fold CV. This approach involves randomly k-fold CV dividing the set of observations into k groups, or folds, of approximately equal size. The first fold is treated as a validation set...

Source: Chapter 5.1.3 in Introduction to Statistical Learning by James, Witten, Hastie and Tibshirani.
