Moderators are Staff members of this site who keep order and deal out punishments. They can lock topics, warn you, fine you, and do other scary things if you break the rules.
Modifications are changes to the core Starcraft data files that make a vastly altered game, with new weapons, graphics, attack routines, anything really. If you want to get into modding, I suggest you come down the Modding Assistance forum or read the How to Write a MOD tutorial.
The word "mod" is used interchangeably for both of these terms.[right][snapback]583274[/snapback][/right]
StarCraft has the only community that uses them interchangeably, everyone else says MOD for modification, and Mod for moderator.