A framework where two neural networks, a generator and a discriminator, are trained simultaneously. The generator tries to create data that looks real, while the discriminator tries to distinguish between real and fake data. When a model performs well on training data but poorly on unseen data. Techniques like regularization, dropout, and cross-validation are used to mitigate this. Neural networks have many hyperparameters, like the number of layers, the number of neurons in each layer, the learning rate, etc. Tuning these hyperparameters is crucial for achieving good performance.