Nunjucks is a powerful and flexible templating engine for JavaScript, inspired by Jinja2. It allows developers to create dynamic HTML, XML, and other formats through reusable templates. Nunjucks supports features like template inheritance, auto-escaping, filters, and macros, making it suitable for both server-side rendering with Node.js and client-side rendering in the browser. Its extensibility lets you easily add custom functionality, enabling efficient and maintainable code for a wide range of web development projects.