As far as I know in practice the whole training set is usually split into training, validation and test sets. Training set is used to train the model, validation to tune the parameters and test set to evaluate the model performance. Does the unknown data(for which we don't know the labels) have the specific name?
For example in kaggle competitions we are usually provided with train and test  set and we are required to make a prediction for the test set. But this one is different from . Should I call train_test to  or something different to ?
P.S. Sometimes in the code, I also see "dev" set but I guess this is just for "development" purposes.