What are WordPress Plugins?
A plugin is a small program that, when added to WordPress, interacts with the software to provide some extensibility to the software. Plugins aren’t part of the core software, nor are they software programs themselves. They typically don’t function as standalone software. They do require the host program (WordPress, in this case) to function.
Plugin developers are the people who write these gems and share them with the rest of the world — usually for free. As is WordPress, most plugins are free to anyone who wants to further tailor and customize a site to meet specific needs.
Literally thousands of plugins are available for WordPress — certainly way too many to list. here are just a few examples of things that plugins let you add to your WordPress blog:
E-mail notification: Your biggest fans can sign up to have an e-mail notification sent to them every time you update your blog.
Submit your blog to social networking services: Allow your readers to submit your blog posts to some of the most popular social networking services such as Digg, Twitter, Facebook, and Reddit.
Stats program: Keep track of where your traffic is coming from; which posts on your blog are the most popular; and how much traffic is coming through your blog on a daily, monthly, and yearly basis.