Tensorflow is an open-source platform for machine learning and neural networks. It allows developers to define computational graphs to perform operations on multi-dimensional tensors that represent inputs and outputs. Tensors flow through the graphs to transform data and train models. Google developed Tensorflow and uses it in many of their products for tasks like search, translation, and recommendations. It works by defining the preprocessing, model building, and training phases and can run on CPUs, GPUs, and mobile devices.