CodeIgniter is an open-source software rapid development web framework, for use in building dynamic web
sites with PHP. CodeIgniter is loosely based on the popular model–view–controller (MVC) development pattern.
While controller classes are a necessary part of development under CodeIgniter, models and views are optional.
Codeigniter can be also modified to use Hierarchical Model View Controller which allows developers to maintain modular
grouping of Controller, Models and View arranged in a sub-directory format. CodeIgniter is most often noted for its speed
when compared to other PHP frameworks