The article explores the concept of cross-validation in machine learning, emphasizing its role in evaluating model performance and reducing bias compared to other methods like simple train/test splits. It focuses on the k-fold cross-validation variant, where the dataset is divided into K partitions, and the model is trained on K-1 partitions while tested on the remaining one, iteratively evaluating and averaging the test errors for accuracy assessment. Despite the advantage of producing less biased performance estimates, a notable downside is the increased training time since the model is trained K times. The article provides a practical example using the Scikit-learn library and the KFold class, demonstrating how to implement k-fold cross-validation for a text classifier and highlighting the importance of not using the test set until the experimentation is complete to avoid overfitting. Additionally, it introduces comet.ml, a platform for tracking machine learning experiments, founded by Gideon Mendels.