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.[13] 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.[14] 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.[15][16] 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’.[17]

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.[18] 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.[19][16] 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,[20] magic use,[21] combat,[22] and the effect of the environment on PCs[23]—help the DM to make these decisions. The Dungeon Master may choose to deviate from the published rules[24] or make up new ones as she or he feels necessary.[25]
Release 3.5 of the three core rulebooks
Release 3.5 of the three core rulebooks

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.[26] A Basic Game boxed set contains abbreviated rules to help beginners learn the game.[27]

The only items required to play the game are the rulebooks, a character sheet for each player and a number of polyhedral dice. The current editions also assume, but do not require, the use of miniature figures or markers on a gridded surface, items that were optional in earlier editions.[28] Many optional accessories are available to enhance the game, such as expansion rulebooks, pre-designed adventures and various campaign settings.[29]

Taken from Wikipedia