use of the terms test set and validation set is the one here described. However, in both industry and academia, they are sometimes used interchanged, by considering that the internal process is testing different models to improve (test set as a development set) and the final model is the one that needs to be validated before real use with an unseen data (validation set). "The literature on machine learning often reverses the meaning of 'validation' and 'test' sets. This is the most blatant example of the terminological confusion that pervades artificial intelligence research. Nevertheless, the important concept that must be kept is that the final set, whether called test or validation, should only be used in the final experiment. Cross-validation In order to get more stable results and use all valuable data for training, a data set can be repeatedly split into several training and a validation datasets. This is known as cross-validation. To confirm the model's performance, an additional test data set held out from cross-validation is normally used. See also Statistical classification List of datasets for machine learning research Hierarchical classification References Datasets in machine learning Validity (statistics)