CNN Diagram is a diagram used to illustrate the structure and components of a Convolutional Neural Network (CNN). There is an example which shows the activation function ReLU. The diagram begins with the input layer, which represents the raw data that is fed into the network. This layer is followed by a set of convolutional layers, which are responsible for extracting features from the input data. It allows researchers and developers to analyze the network's behavior, identify potential problems, and optimize its performance.