See also: How to manage plugins
A juju plugin is an external command that works with juju but which is not part of the juju core code.
At a more technical level, a juju plugin is any executable file in your $PATH that begins with juju-. Although you can run these independently of the Juju command line (juju-<plugin-name>), Juju will also wrap these commands so they can be run within Juju (juju <plugin-name>).
See more: