Keras is an open-source library of high-level neural networks written in Python. It allows developers to quickly create and prototype deep learning models, as well as run them on both CPUs and GPUs. Keras is designed to make developing deep learning models fast and easy, while still being powerful and flexible. It supports a range of different architectures, including convolutional neural networks (CNNs), recurrent neural networks (RNNs), and long short-term memory networks (LSTMs).