The ONNX or Open Neural Network eXchange is an open standard and format to represent machine learning models. ONNX defines a common set of operators and a common file format to represent deep learning models in a wide variety of frameworks, including PyTorch and TensorFlow.
pseudo ONNX graph, visualized with NETRON
When a model is exported to the ONNX format, these operators are used to construct a computational graph (often called an intermediate representation) which represents the flow of data through the neural network.
Important: ONNX Is not a Runtime ONNX is only the representation that can be used with runtimes like ONNX Runtime. You can find a list of supported accelerators here.
Learn more about ONNX.