Geo-Mod
Geometrical Modification (or Geo-Mod for short) means, in short, the ability to modify geometry in real-time. Geo-Mod has been a icon of the Red Faction series since the start.
Engine
The game engines powering Red Faction and Red Faction II are both called the "Geo-Mod engine". This is believed to be as a result of the series icon being the development of very powerful Geo-Mod technology.