WordPress is a lot of things to a lot of different people. It started out as a blogging platform, but has quickly evolved into being one of the most dominant open-source content management systems that runs everything from a personal blog to a major news publication. The main catalyst for this increase in functionality and scope: plugin development!
A plugin is an add-on that can extend the functionality of a WordPress website. It can be as simple as adding some text that quotes “Hello Dolly” to your website, or as complex as adding a paid content subscription wall. Chances are good that whatever function you need for your website, it is available for free, or a minimal cost.