What is the difference between test set and validation set?

I found this confusing when I use the neural network toolbox in Matlab. It divided the raw data set into three parts: training set validation set test set I notice in many training or learning algorithm, the data is often divided into 2 parts, the training set and the test set. My questions are: what is the difference between validation set and test set? Is the validation set really specific to ne

[yukirelax]

トレーニングセット、バリデーションセット

[quanon]

バリデーションセットとテストセットをわざわざ分ける理由は、このページの回答がすごく分かりやすい。