TensorFlow is an open source Python-based machine learning framework developed by Google. It defines computations as data flow graphs where nodes represent operations and edges represent the multidimensional data arrays (tensors) communicated between them. TensorFlow is useful for neural networks and deep learning, as it can efficiently run optimized C++ code on large datasets. Popular applications include image classification, language processing, and machine translation. Many large companies like Google, DeepMind, and Uber use TensorFlow in production systems and research.