In artificial neural networks, the hidden layer is a series of artificial neurons that processes the inputs received from the input layers before passing them to the output layer. An example of a neural network utilizing a hidden layer is the feedforward neural network.[1]
The hidden layers transform inputs from the input layer to the output layer. This is accomplished by applying what are called weights to the inputs and passing them through what is called an activation function, which calculate input based on input and weight. This allows the artificial neural network to learn non-linear relationships between the input and output data.
The weighted inputs can be randomly assigned. They can also be fine-tuned and calibrated through what is called backpropagation.[2]