DOOM is one of the first popular first-person shooter games. Published in 1993, its graphics are top-of-the-line for its time. Multiple sequels were released throughout the 1990s, and the game is probably responsible for many of the conventions of the first-person shooter genre.
There are less than 300 entries about DOOM in the Pit, marking it as a small fanfiction section. Badfic is not incredibly prolific, but there are far more bad game mods than badfic. When badfic does exist, it usually manifests as "I got sucked into DOOM" or "normal person has to live out DOOM" fic. Bad slash is not unheard of, though, which is fairly disgusting when the nature of the game is considered.
Not to be confused with the general concept of doom, which means the general destruction and end of whatever it is applied to. The word "doom" is also screamed by fangirls overzealously attached to the cartoon Invader Zim. In fact, those not attached to Invader Zim also sometimes scream and babble it, thinking it is humorous... without even knowing where it came from.