Die roll fudging is reporting the roll of a die to be something other than what it was.
When a player fudges a die roll, this is generally considered cheating. Sometimes, the occasional fudge may be tolerated. In most groups, though, players are not permitted to change die rolls.
Can the GM cheat?Edit
In some conceptions of the GM role, it is impossible to cheat. The GM controls the universe, including the significance of any die roll. Hence, changing a die roll to suit some greater purpose is just part of their job. This may be done for dramatic reasons, to increase fun, or to be kind to a player who has had a run of bad luck.
On the other hand, other people consider GM die rolls to be just as important as player rolls in creating genuine tension and chance in a game. In this view, the GM is free to set ground rules, but they must abide by those rules, including results suggested by the dice. GMs should be advised that many players feel strongly about this viewpoint. If they discover the GM has been fudging, they may become disillusioned or upset.
Fudging for a specific purposeEdit
GMs sometimes fudge die rolls in order to avoid anticlimax, favor the PCs, favor the NPCs, or to direct a particular outcome they think is dramatically appropriate.
Fudging to disguise fiatEdit
Sometimes, a GM will roll a die, even though they have already decided on something. The GM may reserve their use of the GM fiat for dramatic or game purposes, allowing the dice to dictate how a scenario plays out. In this case, the GM is not really fudging a die, but engaging in GM obfuscation. If this is done frequently, players may (justifiably) complain of railroading.