An online multiplayer game
(OMG) is a video game that can be played over the Internet against other players. These types of games can only be played over the Internet, and must involve multiple users. They can be played on a single gaming platform or be capable of being played on a variety of gaming platforms and therefore could be considered a platform unto itself.
Online multiplayer games is an encapsulation of many other popular types of games. It is a master category for the likes of:
MMORPG - Massively-Multiplayer online RPG
MMORTS - Massively-Multiplayer Real-Time strategy game
Multiplayer is a mode of play for computer and video games in which multiple people can play the same game at the same time. Unlike most other games, computer and video games are often single-player activities because the computing power exists to create artificial opponents.
In most multiplayer games, players compete against each other in a test of skill. There are some games in which players ally to achieve a common goal, and in others, groups of players form teams which fight as a group.
Usually multiplayer games either use computer networking to allow players to play together or require the players to gather around a single game system to play.