2.5D in the context of "Doom (1993 video game)"

A first-person shooter (FPS) is a video game centered on gun fighting and other weapon-based combat seen from a first-person perspective, with the player experiencing the action directly through the eyes of the main character. This genre shares multiple common traits with other shooter games, and in turn falls under the action games category. Since the genre's inception, advanced 3D and pseudo-3D graphics have proven fundamental to allow a reasonable level of immersion in the game world, and this type of game helped pushing technology progressively further, challenging hardware developers worldwide to introduce numerous innovations in the field of graphics processing units. Multiplayer gaming has been an integral part of the experience and became even more prominent with the diffusion of internet connectivity in recent years.

Although earlier games predate it by 20 years, Wolfenstein 3D (1992) was the highest-profile archetype upon which most subsequent first-person shooters were based. One such game, considered the progenitor of the genre's mainstream acceptance and popularity, was Doom (1993), often cited as the most influential game in this category; for years, the term "Doom clone" was used to designate this type of game, due to Doom's enormous success. Another common name for the genre in its early days was "corridor shooter", since processing limitations of that era's computer hardware meant that most of the action had to take place in enclosed areas, such as corridors and small rooms.