I just stumbled over the expression NxN- fold cross validation and i am not sure what it's exact meaning.
N-fold cross validation, as i understand it, means we partition our data in N random equal sized subsamples. A single subsample is retained as validation for testing and the remaining N-1 subsamples are used for training. The result is the average of all test results.
Now my question is what does NxN-fold cross validation mean?