What is the difference between a mod, a plugin, and an addon?

[Lefty]

I hear the three used interchangably, but some games call them mods, some call them addons, and most non-game software call them plugins. Is there a difference?

[Chibbity]

Nope.

[Rhomphaia]

Mostly they are used interchangeably.
It could be argued that mod is the umbrella term, and there is a difference between plugin and addon as to how they effect their respective modifications, but if you ask 4 people what the difference is you will get 5 different answers back.

[desrtfox071]

For KSP, technically, a plugin is a part of a mod - specifically the library aka .dll portion. Not all ksp mods have plugins. I agree that really, the terms are used interchangeably.

[Lefty]

ahh... that makes sense i guess