A web application framework is a software framework that is designed to support the development of dynamic websites, Web applications and Web services.
CodeIgniter: an open source Web Application Framework that helps you write PHP programs
Based on an innovative architecture, Symfony is fast, flexible, and easy to learn. It allows developers to build better and more easily maintainable websites with PHP.
CakePHP is a rapid development framework for PHP that provides an extensible architecture for developing, maintaining, and deploying applications. Using commonly known design patterns like MVC and ORM within the convention over configuration paradigm, CakePHP reduces development costs and helps developers write less code.