Modules

From NWN1 Custom Content Guide

MOD is short for module or modification depending on the context of its usage.

Module will refer to a file residing in /nwn/modules/ that holds the scripts, conversations and areas of an adventure. This is what you load when you want to play a NWN game.

Modification refers to changes to the game rule system, graphics and such that drastically alters the way the game behaves. The most popular mod will be Counter-Strike for Half-Life.