Fudge dice are the dice that are used for the Fudge generic roleplaying game. Unlike most other RPGs, Fudge dice do not have numbers. Instead, each six sided die has either a plus sign, minus sign, or is blank:
A variable number of dice are rolled, but typically four of them. For this reason Fudge dice come in sets of 4 dice to a set. The idea behind the dice is that you add every plus symbol, and subtract every minus symbol (ignoring the blanks). This results in a modifier from -4 to +4.
Because Fudge dice are non-standard and the Fudge system is vastly less played than, say, every other RPG combined, there aren't a whole lot of Fudge dice manufactured, and the cost of the dice is higher than standard numbered dice due to economies of scale.