TensorFlow is Google's open-source machine learning framework designed for building, training, and deploying neural networks at scale. It combines low-level tensor operations with high-level Keras APIs, making it suitable for both research and production. TensorFlow runs on CPUs, GPUs, and TPUs, supports distributed training, and enables deployment to mobile, web, edge devices, and servers. The key mental model: TensorFlow builds computational graphs where nodes represent operations and edges represent tensors flowing between them, with automatic differentiation handling backpropagation for training.