Wikipedia WoQT incoming!
Casual gamer
A casual gamer is a player whose time or interest in playing games is limited. Casual gamers tend to play games designed for ease of gameplay and don't spend much time playing more involved games. The genres that casual gamers play vary, and they might not own a specific video game console to play their games. Casual gamer demographics vary greatly from those of other video gamers, as the typical casual gamer is older and more predominantly female. One casual gamer subset is the "fitness gamer", who plays motion-based exercise games.

The term casual gamer can be used to distinguish between play styles of level-based character advance in nonlinear games with respect to the amount of dedicated hours of play. MMORPGs may require many hours of grinding to develop a character to maximum level and reach the endgame, and are thus not typically suited for casual gaming. However, games like DOFUS, Eve Online and The Lord of the Rings Online try to balance leveling between any casual gamers and those dedicating more hours to the game.
Mid-core gamer

A core or mid-core gamer is a player with a wider range of interests than a casual gamer and is more likely to enthusiastically play different types of games, but without the amount of time spent and sense of competition of a hardcore gamer. The mid-core gamer enjoys games but may not finish every game they buy, doesn't have time for long MMO quests, and is a target consumer. Nintendo president Satoru Iwata stated that they designed the Wii U to cater to core gamers who are in between the casual and hardcore categories.

A number of theories have been presented regarding the origins of mid-core gamers. James Hursthouse, the founder of Roadhouse Interactive credits the evolution of devices towards tablets and touch-screen interfaces, whereas Jon Radoff of Disruptor Beam compares the emergence of mid-core games to similar increases in media sophistication that have occurred in media such as television.
Hardcore gamer
See also: Video game addiction

Hardcore gamers extend gaming into their lifestyle and may represent the stereotypical “game geek”. They are frequent purchasers of games, prefer to expend significant time on games, and are more likely to try to "master" their games by completing as many objectives as possible. Hardcore gamers may take part in video game culture such as competitions, events and conventions. Competitions may involve organized tournaments, leagues, or ranked play integrated into the game. An example of this is Major League Gaming, an electronic sports organization that often holds events for first-person shooter games such as Quake. There are many subtypes of hardcore gamers based on the style of game, gameplay preference, hardware platform, and other preferences.