Immersion, in the context of the digital environment and reality gaming, is when a person becomes so engaged and focused on a task that they cease to be aware of their presence in the physical world. This immersion is due to the nature of the digital environment or the game, which are often designed with such detail and complexity that they become a world within themselves. Immersion is particularly commons with MMOs because of the endless possibilities within a virtual world (see Second Life). For example, in the game World of Warcraft, a person becomes so invested in their avatar's actions, that they almost become that character. The game is specifically designed to create this sense of immersion.
Related to immersion is the concept of "flow," which refers to the idea that after a certain amount of time playing games, the user becomes fully engaged and "in the zone," where the user disengages from the world around and becomes fully immersed in the game. It can be similar to the experience that sports players feel when they are fully enveloped the game they are playing, where outside influences become miniscule compared to the action at hand.