CodeIgniter is a powerful PHP framework designed for developing web applications quickly and efficiently. It follows the Model-View-Controller (MVC) architectural pattern, promoting a clear separation between data handling, user interface, and business logic. CodeIgniter is known for its lightweight footprint, ease of use, and straightforward setup, making it an ideal choice for beginners and experienced developers alike. It offers built-in libraries for common tasks such as database interaction, session management, and form validation, enabling rapid application development while maintaining flexibility and performance.