Dice
Dice (singular: die) are high-impact polyhedra, usually having four, six, eight, ten, twelve, twenty or one hundred 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 gripping hand, some games don't use dice at all! These tend to be relatively new games like Nobilis or Amber.
Really, really ancient gamers remember Crayola Dice.
/tg/ has a dice-rolling function. Simply type dice+XdY+Z or dice XdY Z (the Z is optional) into the email field to roll X dice with Y sides and add a modifier Z.