Dice
Dice are high-impact polyhedra, usually having four, six, eight, ten, twelve or twenty faces. In role-playing games and tabletop war games, they are used as randomizers to inject an element of chance into the game. Non-gamers often only know about the six-sided die (hereafter referred to as the d6) thanks to the ubiquity of games like Monopoly and Yahtzee. Which dice are used tends to vary by system, Dungeons and Dragons makes use of all types. On the other hand White Wolf games and Classic Traveller use only ten- and six-sided dice, respectively. On the the gripping hand, some games don't use dice at all! These tend to be relatively new games like Nobilis or Amber.
/tg/ has a dice-rolling function. Simply type dice+XdY+Z or dice XdY Z (the Z is optional) to roll X dice with Y sides and add a modifier Z.