For the purposes of this project we use the word modding in a bit more broader sense than usual. Usually modding, as in modification, revolves around modification of data that's already well structured and used to feed an existing set of structures baked into an executable.
Our system is more open ended. Modding is closer to modeling, and it's about creating simulation structures almost "from scratch", without content hard-coded into the executable. Of course that's not to say this approach is always superior. It's just more flexible on the user level and potentially allows for some interesting developments.