Fudge is a generic role-playing game (or a role playing game that can be used in any genre). Fudge at first was an acronym and stood for "Freeform Universal Donated Gaming Engine" (the "Donated" part was changed to "Do-it-yourself"), but this was dropped. Unlike other generic role-playing games like GURPS or the d20 System, Fudge allows people to build their own specialized RPG.
The Game Master can choose what attributes and skills will be used. These are rated on the following scale: terrible, poor, mediocre, fair, good, great and superb. They also choose Gifts and Faults. The game also uses specialized dice. They have plus, minus and blank sides. These four of these dice are rolled. For every "+", you go up a step higher (ex: fair to good). For every "-", you go a step lower (ex: great to good). Blanks do nothing. You do this for every trait.
The rules of Fudge are customizable so the game can be complex or simple. However, the rules (overall) encourage role-playing over the rules. In fact, the game encourages players to "Just Fudge It", which means focus less on the rules and more on the story.
My source was Wikipedia.