Dungeons & Dragons

Dungeons and Dragons (often abbreviated to "D&D") is the oldest and one of the most popular Pen and paper role-playing games. Each player creates a character within the game, and tells the referee, or Dungeon Master, what they will do. Each character belongs to a class, of which there are a number to choose from. The original D&D game was released in 1974. The 4th Edition, which involved major changes to the underlying game system, was released in November 2008. The classes in 4th edition are as follows:

Cleric, a priest of sorts, with the ability to summon the power of their deity/poewr source
Fighter, a martial, non-magical warrior
Paladin, a champion of a specific deity
Ranger, a two-weapon or ranged weapon specialist
Rogue, equivalent of a thief
Warlock, a user of dark magic
Warlord, a commander who leads from the front
Wizard, a wielder of mystical powers

The Dungeon Master, who runs the game, has a number of responsibilities. He must create or buy the adventures, play the monsters, keep the game balanced, keep the players in control, and overall, make sure the players are having fun.

The game is played with polyhedral dice containing many different numbers and are referred to by "d + number of sides", i.e. d6 is a six sided die, d20 is a twenty sided die. The dice used are d4s, d6s, d8s, d10s, d12s (rarely used), and d20s. A special d10, which contains multiples of 10 from 0 to 90, is rolled in conjunction with a standard d10 to produce the equivalent of a d100.

D&D falls into the "d20" game system, and just so happens to use that die quite frequently.