The Zend Framework is a PHP web application framework that provides modular, reusable PHP components for common web development tasks like database access, caching, session handling, and internationalization. It includes an MVC framework, database abstraction layer, authentication, and many other components. The framework is free, open source, and has over 150,000 lines of code with 90% unit test coverage. It aims to provide simple, extensible solutions to common problems in web development.