The best definition of a neural network is provided by an inventor, Dr. Robert Hecht-Nielsen, one of the first neurocomputer scientists, in Neural Network Primer: Part I by Maureen Caudill, AI Expert, Feb. 1989:
The fundamental building blocks of neural networks are neurons, and they are organized in different layers. The tiered architecture has the neurons in each layer connected to neurons in the next layer. A neural network has, at a minimum, three layers. The input layer is connected to one or more hidden layers, where the connection is ...