Massively multiplayer online role-playing game (MMORPG) is a genre of computer role-playing games in which a very large number of players interact with one another within a virtual game world.

As in all RPGs, players assume the role of a character (often in a fantasy world) and take control over many of that character's actions.MMORPGs are distinguished from single-player or small multi-player RPGs by the number of players, and by the game's persistent world, usually hosted by the game's publisher, which continues to exist and evolve while the player is away from the game. This is often referred to as being offline.

MMORPGs are played throughout the world. Worldwide revenues for MMORPGs exceeded half a billion dollars in 2005,and Western revenues exceeded US$1 billion in 2006. In 2008, Western consumer spending on subscription MMOGs grew to $1.4 billion.World of Warcraft, a popular MMORPG, had over 12 million subscribers as of October, 2010.

 Although modern MMORPGs sometimes differ dramatically from their antecedents, many of them share some basic characteristics. These include several common themes: some form of progression, social interaction within the game, in-game culture, system architecture, and character customization. Characters can often be customized quite extensively, both in the technical and visual aspects, with new choices often added over time by the developers. Many games also offer some form of modding in order to allow for even greater flexibility of choice.

Character abilities are often very specific due to this. Depending on the particular game, the specialties might be as basic as simply having a greater affinity in one statistic, gaining certain bonuses of in-game resources related in-game race, job, etc.

 The majority of popular MMORPGs are based on traditional fantasy themes, often occurring in an in-game universe comparable to that of Dungeons & Dragons. Some employ hybrid themes that either merge or substitute fantasy elements with those of science fiction, sword and sorcery, or crime fiction. Still others draw thematic material from American comic books, the occult, and other genres. Often these elements are developed using similar tasks and scenarios involving quests, monsters, and loot. Another popular theme in MMORPGs is the past/future. Oftentimes, in the past, you are a character who fights mythical monsters such as dragons, demons, and sorcerers. While in the future, you fight mechanical beasts such as robots or cyborgs as well as alien life forms.

   In nearly all MMORPGs, the development of the player's character is a primary goal. Many MMORPGs feature a character progression system in which players earn experience points for their actions and use those points to reach character "levels", which makes them better at whatever they do.Traditionally, combat with monsters and completing quests for NPCs, either alone or in groups, are the primary ways to earn experience points. The accumulation of wealth (including combat-useful items) is also a way to progress in many MMORPGs, and again, this is traditionally best accomplished via combat. The cycle produced by these conditions, combat leading to new items allowing for more combat with no change in gameplay, is sometimes pejoratively referred to as the level treadmill, or 'grinding'. The role-playing game Progress Quest was created as a parody of this trend.

 MMORPGs almost always have tools to facilitate communication between players. Many MMORPGs offer support for in-game guilds or clans (though these will usually form whether the game supports them or not).

In addition, most MMOs require some degree of teamwork for parts of the game. These tasks usually require players to take on roles in the group, such as those protecting other players from damage (called tanking), "healing" damage done to other players or damaging enemies.

MMORPGs generally have Game Moderators or Game Masters (frequently abbreviated to GM), which may be paid employees or unpaid volunteers who attempt to supervise the world. Some GMs may have additional access to features and information related to the game that are not available to other players and roles.

 Most MMORPGs provide different types of classes that players can choose. Among those classes, players are encouraged to roleplay their characters, providing rules, functionality and content to this end. Some MMORPGs offers "roleplay-only" servers that prohibit interactions to other players among characters for those who want to immerse themselves in the game in this way. Community resources such as forums and guides exist in support of this play style.

For example, if a player wants to play a priest role in his MMORPG world, he might buy a cope from a shop and learn priestly skills, proceeding to speak, act, and interact with others as their character would. This may or may not include pursuing other goals such as wealth or experience. Guilds or similar groups with a focus on roleplaying may develop extended in-depth narratives using the setting and resources of the game world. Some MMORPG's have gone so far as to provide whole server's specified for the roleplaying orientated player so that they can immerse themself fully in the universe they have created.

 Since MMORPGs have so many elements in common, and those elements are experienced by so many people, a common all players, and this has led players of many games to expect "buffing" or "nerfing", which describe the strengthening or weakening, respectively, of particular game elements. ("Buffing" also refers to in-game effects that temporarily enhance performance; both usages come from a core meaning of increasing power levels.)

As another example, in many older MMORPGs the fastest way to progress was simply by killing the same monsters over and over again, and as this is still common in the genre, all MMORPG players know the process as "grinding", or "camping" (sitting at a monster's spawn point in order to attack it as soon as it respawns). The importance of grinding in MMORPGs, and how much "fun" it contributes to the experience, is constantly debated. Many MMORPGs have taken steps to eliminate or reduce grinding, but few such attempts have met with success, and it is generally accepted by players and developers alike that some amount of 'grind' is required to maintain a stable playing experience.

MMORPG addiction, which has been a source of concern for parents, also affects the culture. Some players might look down on those who invest huge amounts of time and or money into a game, while others might scorn those who can't put in the time to "play properly". The validity of such viewpoints is heavily debated, with both sides of the issue being discussed frequently on most games' forums.

Most MMORPGs are deployed using a client–server system architecture. The server software generates a persistent instance of the virtual world that runs continuously, and players connect to it via client software. The client software may provide access to the entire playing world, or further 'expansions' may be required to be purchased to allow access to certain areas of the game. EverQuest and Guild Wars are two examples of games that use such a format. Players generally must purchase the client software for a one-time fee, although an increasing trend is for MMORPGs to work using pre-existing "thin" clients, such as a web browser.

Some MMORPGs require payment of a monthly subscription to play. By nature, "massively multiplayer" games are always online, and most require some sort of continuous revenue (such as monthly subscriptions and advertisements) for maintenance and development. Some games, such as Guild Wars, have disposed of the 'monthly fee' model entirely, and recover costs directly through sales of the software and associated expansion packs. Still others adopt a micropayment model where the core content is free, but players are given the option to purchase additional content, such as equipment, aesthetic items, or pets. Games that make use of this model often have originated in Korea, such as Flyff and MapleStory. This business model is alternately called "pay for perks" or "freemium", and games using it often describe themselves with the term "free-to-play".

Depending on the number of players and the system architecture, an MMORPG might actually be run on multiple separate servers, each representing an independent world, where players from one server cannot interact with those from another; World of Warcraft is a prominent example, with each separate server housing several thousand players. In many MMORPGs the number of players in one world is often limited to around a few thousand, but a notable example of the opposite is EVE Online which accommodates several hundred thousand players on the same server, with over 60,000 playing simultaneously (June 2010) at certain times. Some games allow characters to appear on any world, but not simultaneously (such as Seal Online: Evolution), others limit each character to the world in which it was created. World of Warcraft has, however, experimented with "cross-realm" (i.e. cross-server) interaction in PvP battlegrounds, using server clusters or "battlegroups" to co-ordinate players looking to participate in structured PvP content such as the Warsong Gulch or Alterac Valley battlegrounds.Additionally, in the recent patch 3.3, released on December 8, 2009, introduced a cross-realm "looking for group" system to help players form groups for instanced content (though not for open-world questing) from a larger pool of characters than their home server can necessarily provide.

  The term MMORPG was coined by Richard Garriott, the creator of Ultima Online, in 1997.Previous to this and related coinages, these games were generally called graphical MUDs; the history of MMORPGs traces back directly through the MUD genre. Through this connection, MMORPGs can be seen to have roots in the earliest multi-user games such as Mazewar (1974) and MUD1 (1978). 1985 saw the release of a roguelike (pseudo-graphical) MUD called Island of Kesmai on CompuServe and Lucasfilm's graphical MUD Habitat. The first fully graphical multi-user RPG was Neverwinter Nights, which was delivered through America Online in 1991 and was personally championed by AOL President Steve Case.Other early proprietary graphical online RPGs include three on The Sierra Network: The Shadow of Yserbius in 1992, The Fates of Twinion in 1993, and The Ruins of Cawdor in 1995. Another milestone came in 1995 as NSFNET restrictions were lifted, opening the Internet up for game developers, which allowed for the first truly "massively"-scoped titles. Finally, MMORPGs as defined today began with Meridian 59 in 1996, innovative both in its scope and in offering first-person 3D graphics, with The Realm Online appearing nearly simultaneously.Ultima Online, released in 1997, is often credited with first popularizing the genre,though more mainstream attention was garnered by 1999's EverQuest in the West and 1996's Nexus: The Kingdom of the Winds in Asia.

These early titles' financial success has ensured competition in the genre since that time. MMORPG titles now exist on consoles and in new settings, and their players enjoy higher-quality gameplay. The current market for MMORPGs has Blizzard Entertainment's World of Warcraft dominating as the largest pay-to-play MMORPG, alongside earlier such titles like Final Fantasy XI and Phantasy Star Online, though an additional market exists for free-to-play MMORPGs, which are supported by advertising and purchases of in-game items. This free-to-play model is particularly common in Korean MMORPGs such as MapleStory, Rohan: Blood Feud, and Atlantica Online. Also, there are some free-to-play games, such as RuneScape & Tibia, where the game is free, but one would have to pay monthly to play the game with more features. Guild Wars is an exception. It avoids competition with other MMORPGs by only requiring the initial purchase of the game to play.

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