Underneath the huge overarching genre of MMOG, there are subgenres that branch off and are gaining popularity in and of themselves. A few of them are listed below.

This stands for “massively multiplayer online role-playing games.” MMORPGs are probably the most popular type of MMOG. They are huge online computer role-playing games that allow large populations of players to interact with each other in a cooperative or competitive manner, or both at the same time. Each player's character wears an avatar, or a visual representation of what their character looks like. Players roam vast virtual worlds that are always changing, where they can meet old and new virtual characters as friends or foes and act out a number of actions, including killing, purchasing items, and carrying conversations with other characters.

Most MMORPGs require players to either buy client software for a one-time payment or pay a monthly subscription fee in order to have access to the game's virtual worlds.

This stands for “massively multiplayer online first-person shooter.” These are computer games that allow players to engage in individual or team combat. They also utilize experience points in order to keep the games more engaging on a long-term basis for players who want to see their character develop. Due to the demanding requirements of these games, players with slower computers may lag on their server, slowing down their gameplay and making it difficult to enjoy the full gamut of the game's entertainment experience. These games also require monthly fees in order to pay for server upkeep and troubleshooting staff.

This stands for “massively multiplayer online real-time strategy.” These games combine real-time strategy with the ability to play with huge numbers of players online at the same time. They allow the players to control their forces overhead.

BBMMORPG

This lengthy series of letters stands for “browser-based massive multiplayer online role-playing games.” These are played through Internet browsers, which allow both developers and players to avoid the costs and hassles of creating and downloading clients. They have 2D graphics or are text-based, and utilize browser plugins and extensions.

These “mobile massive multiplayer online games” are games that are played using mobile devices such as cellular phones or pocket PCs.