DM means Dungeon Master. I think it's usually used to refer to the person who runs aDungeons and Dragons campaign, while some other systems call them game master.
I never fudge rolls. But the competency of the enemies' tactics depend on how well the party is doing. I try to make encounters difficult enough to barely avoid a party wipe.
Where do I fall if I kill them all, turn then into vampires and send them on a quest to uncurse themselves before they level and become vampires forever?