Fudge dice are "zero centered" dice, with negative numbered rolls equaling positive ones. The most common Fudge dice have two sides showing a plus sign, two showing a minus sign and two blank sides.
Fudge dice nomenclature is usually of the form "Roll NdF." This means roll N Fudge Dice and add the results. For instance, rolling 3dF and showing + 0 0 is a +1 result, while rolling 4dF that show + 0 - - results in a -1. For any roll of NdF, the average roll is always zero, the range is -N to +N. 1dF has a uniform distribution, 2dF has a triangle distribution, and NdF for N > 2 has a normal distribution, with less variance as N increases.