A jQuery plugin is simply a new method that we use to extend jQuery's prototype
object. By extending the prototype object you enable all jQuery objects
to inherit any methods that you add. Once the plugin is established,
whenever you call $() you're creating a new jQuery object, with your
plugin now method included along with all of jQuery's existing methods.
The idea of a plugin is to do something with a collection of elements.
You could consider each method that comes with the jQuery core
a plugin, like fadeOut or addClass.
You can make your own plugins and use them privately in your
code or you can release them into the wild. There are thousands
of jQuery plugins available online. The barrier to creating a plugin
of your own is so low that you'll want to do it straight away!