The correct answer is: D. Combining multiple models to improve predictive performance.
Ensemble learning is a machine learning technique that combines the predictions of multiple models to improve the overall accuracy of the predictions. This can be done by averaging the predictions of the models, or by using a voting scheme to select the most likely prediction. Ensemble learning can be used to improve the accuracy of predictions for a variety of tasks, such as classification, regression, and forecasting.
Option A is incorrect because it describes a single model, not multiple models. Option B is incorrect because it describes a visualization technique, not a machine learning technique. Option C is incorrect because it describes a data preprocessing technique, not a machine learning technique.