Dungeons & Dragons (D&D)  is a fantasy role-playing game (RPG)

D&D assigns each player a specific character to play. These characters embark upon imaginary adventures within a fantasy setting. A Dungeon Master serves as the game’s referee and storyteller, while also maintaining the setting in which the adventures occur. The characters form a party that interacts with the setting’s inhabitants (and each other). Together they solve dilemmas, engage in battles and gather treasure and knowledge. In the process the characters earn experience points to become increasingly powerful over a series of sessions.

Dungeons & Dragons is a structured yet open-ended role-playing game. It is normally played indoors with the participants seated around a table-top. Typically, each player controls only a single character, which represents an individual in a fictional setting. When working together as a group, these player characters (PCs) are often described as a ‘party’ of adventurers, with each member often having his or her own areas of specialty that contributes to the success of the whole. During the course of play, each player directs the actions of his or her character and its interactions with the other characters in the game. A game often continues over a series of meetings to complete a single adventure, and longer into a series of related gaming adventures, called a ‘campaign’.

The results of the party’s choices and the overall storyline for the game are determined by the Dungeon Master (DM) according to the rules of the game and the DM’s interpretation of those rules.The DM selects and describes the various non-player characters (NPCs) the party encounters, the settings in which these interactions occur, and the outcomes of those encounters based on the players’ choices and actions. Encounters often take the form of battles with ‘monsters’ – a generic term used in D&D to describe potentially hostile beings such as animals or mythical creatures. The game’s extensive rules – which cover diverse subjects such as social interactions, magic use, combat, and the effect of the environment on PCs – help the DM to make these decisions. The Dungeon Master may choose to deviate from the published rules or make up new ones if he or she feels it is necessary.

The most recent versions of the game’s rules are detailed in three core rulebooks: The Player’s Handbook, the Dungeon Master’s Guide and the Monster Manual. The only items required to play the game are the rulebooks, a character sheet for each player and a number of polyhedral dice. You can also use of miniature figures or markers on a gridded surface. Many optional accessories are available to enhance the game, such as expansion rulebooks, pre-designed adventures and various campaign settings.

Source: wikipedia.org