To extend the functionality of WordPress, WordPress Plugins are composed of php scripts. They can offer new features to your blog that either add otherwise unavailable new additions or enhance features that were already available on your site.
Most of WordPress users require a few Plugins, such as Plugins dealing with customized post listings or comment spam protection. Other people enjoy the featured Plugins which provide post word counts, frequently updated weather reports, rating systems, etc. WordPress Plugins are they are not incorporated into the core of WordPress since they are optional and based upon the needs of the user.