feed-forward neural networks where is referred to as an activation function although variety of activation functions can be usedas we shall see later in the non-linear function is generally used figure - shows detailed look at the unit figure - unit in neural network the overall structure of neural network neural networks are constructed using the unit as basic building block these units are organized as layerswith every layer containing one or more units the last layer is referred to as the output layer all layers before the output layers are referred to as hidden layers the first layerusually referred as the th layeris the input layer each layer connects to the next successive layer with weightswhich are trained/updated in an iterative way