What Are WordPress Plug-Ins?
WordPress plug-ins are functions written in php (a scripting language) that can extend the capabilities of your WordPress blog or website. Developers create both free and paid WordPress plug-ins, and you can access a huge variety of WordPress plug-ins in the WordPress Plugin Directory at wordpress.org/extend/plugins
Some WordPress plug-ins come preinstalled with WordPress, but most must be uploaded individually to your WordPress plug-ins folder. Some might be included as part of a theme upload, as discussed in Chapter 17.
Plug-ins are what set WordPress apart from other blogging applications because they add so much more functionality above and beyond traditional blogging features, other blogging applications ...