Ionic is an open-source framework used for building cross-platform mobile applications using web technologies like HTML, CSS, and JavaScript. It allows developers to create high-quality mobile apps that can run on both iOS and Android devices from a single codebase. With its rich library of pre-built components and tools, Ionic simplifies the development process and enhances user experience. The framework is built on top of Angular and Apache Cordova, making it a popular choice for developers looking to leverage their web development skills in mobile app creation.