What's a Plug-in?

Plug-in

Pros and Cons
A macro, which empowers it's host program. 'Make Inkscape cut'
It works like a genuine part of its host program either as a toolbar or a submenu.

Example:  

Sign Programm

Pros and Cons
A plug-in's counterpart is a sign program.
A sign program includes plotter drivers with all tools for designing, editing and cutting of signmaking jobs. Unlike with the classic illustration programs such as CorelDraw and Illustrator, all tools are tailored to the special requirements of signmakers.

Example: