A Graph neural network (GNN) is a class of artificial neural networks for processing data that can be represented as graphs. In the more general subject of "Geometric Deep Learning", certain existing neural network architectures can be interpreted as GNNs operating on suitably defined graphs. Convolutional neural networks, in the context of computer vision, can be seen as a GNN applied to graphs structured as grids of pixels. Transformers, in the context of natural language processing, can be seen as GNNs applied to complete graphs whose nodes are words in a sentence.