Keras is a popular open-source library for deep learning which provides a simple and powerful Python API that simplifies the development of deep learning models. It is built on top of the powerful TensorFlow library and is designed to enable quick experimentation with deep neural networks. It allows developers to easily create and iterate on models without having to worry about the underlying details of the algorithms. With Keras, developers can quickly build and deploy complex machine learning models with minimal effort. Keras also provides a range of helpful tools such as data preprocessing, visualization, and more. It's no wonder why Keras is so popular with developers – it provides an easy-to-use interface for quickly building and deploying powerful deep learning models.