What is a WordPress plugin?

A plugin is an "add on" for WordPress that brings a new feature to the way WordPress works.  Out of the box WordPress comes with everything you need for most websites.  However, sometimes you may want to do something differently or add stuff that WordPress doesn't do natively.  That's where plugins come in.  Organize Series is a plugin for WordPress.  All the Organize Series Add-ons are WordPress plugins as well with the only difference being that they require Organize Series in order to be activated.