Fastify is a web framework for Node.js that helps developers create high-performance, low-latency REST APIs quickly and easily. It is based on the popular Express.js framework but provides a much more efficient and streamlined approach to building RESTful APIs. Fastify focuses on providing developers with an easy-to-use API that allows them to quickly set up routes and use various plugins to add functionality to their applications. It also has built-in support for JSON Schema validation, logging, authentication, and other common web development tasks.