What is a Plugin? Plugin is a package of files which can be added to your WordPress website. It can be used to extend the core functionality or add new functionality on your WordPress site without modifying the core. A WordPress package can be created with PHP, images, CSS and JS file resources as per your business needs. This Article is Originally Posted on IceCube Digital - Best WordPress Plugin Development Company . Let’s Check out our complete step by step guide on WordPress Plugin Development from Scratch .