A mod is short for Moderator. There can be 3 types of moderators. A forum moderator, game moderator and Global moderator.
The forum moderator or 'forum mod' looks after the forums, the game moderator or 'game mod' looks after the game and the global moderator or 'global mod' looks after both game and forums. What I mean by looking after is 'moderating'. For example banning members that break rules, locking threads, making announcements and keeping the game/forum peaceful c: