Originally written “plug-in,” a plugin is just what the name suggests: a separate module that can be “plugged in” to a WordPress site.
Plugins are actually pieces of software akin to an “app” that extend the functionality of a WordPress site. Plugins are available both via the official WordPress.org website as well as from third-party developers. Plugins do everything from add new features to change how your WordPress site operates, so always be careful before adding a new plugin.
Plugins are written in the PHP programming language. If you have sufficiently well developed coding skills, you can write your own WordPress plugins.
To access your plugins, log into the administration screen. On the left-hand side, click on “Plugins”. From there, you’ll be able to browse for new plugins to install, update, enable/disable existing plugins, or edit the core files of the plugin. You can, if you chose, also install plugins via an FTP client.
Note: If your site is hosted on WordPress.com, you cannot edit, delete, update, or add plugins.
It’s important to remember that most plugins are free and so rarely come with tech support. In addition, there are lots of plugins which promise to perform the same functions, so carefully evaluate a plugin before you download and install it. It’s usually recommended that you only use plugins that are compatible with the version of WordPress that you are using.
If you think that a plugin is slowing down your site, try disabling it. Most of the time, however, a well-written plugin should not slow down your site.
There is no limit to the number of active plugins you can have installed on a WordPress site.