Generalization error

For supervised learning applications in machine learning and statistical learning theory, generalization error^[1] (also known as the out-of-sample error^[2] or the risk) is a measure of how accurately an algorithm is able to predict outcomes for previously unseen data. As learning algorithms are evaluated on finite samples, the evaluation of a learning algorithm may be sensitive to sampling error. As a result, measurements of prediction error on the current data may not provide much information about the algorithm's predictive ability on new, unseen data. The generalization error can be minimized by avoiding overfitting in the learning algorithm. The performance of machine learning algorithms is commonly visualized by learning curve plots that show estimates of the generalization error throughout the learning process.