A plugin is a piece of software including a group of functions that can be contributed to a WordPress website.
http://johncms.com/go.php?url=https://beckettxttz064.page.tl/A-plugin-is-a-piece-of--software-application--consisting-of-a-group-of-functions-that-can-be-added-to-a-WordPress--site-.-.htm
A plugin is a piece of software containing a group of functions that can be contributed to a WordPress website.