"Fudge uses customized "Fudge dice" which have an equal number of plus, minus and blank sides. A number of these dice are rolled, usually four at a time ("4dF" in Fudge dice notation), and for every plus side that comes up the result of using the Trait is considered one step higher (e.g. from Fair to Good) and for every minus side that comes up the result is considered one step lower. The goal is to match or surpass the difficulty level, also on the adjective scale, of the test. Thus, a Good attribute is considered to be Great if you were to roll two plus sides, one minus side, and one blank—the minus side cancels out one of the plus sides and the remaining plus side raises the result by one step. The same Good attribute would be considered Poor if you were to roll three minus sides and one blank.
These dice are also used in Fate games as well as some other game systems."
Source: Wikipedia, "Fudge_dice," available under the CC-BY-SA License.
From the Instructions in a pack of Fudge Dice
Fudge dice are made for the Fudge roleplaying game. A fudge die contains two sides with a plus sign (+), which represent +1; two sides that are blank, which represent 0; and two sides with a minus sign (-), which represent -1. A Fudge die is functionally a three sided die (d3). While most d3s have sides 1,2 and 3, a dF has sides of -1, 0, and +1 - equivalent to a d3-2.