A plugin is a piece of software application including a group of functions that can be added to a WordPress site.
https://www.storeboard.com/blogs/general/a-plugin-is-a-piece-of-software-application-including-a-group-of-functions-that-can-be-contributed-to-a-wordpress-site/1782793
A plugin is a piece of software consisting of a group of functions that can be added to a WordPress site.