A Ghost in the System is a bit of loose programming that developers overlook in a game that makes something strange happen. This has been observed in games most usually like Call of Duty, Halo, and Battlefield. These have been around since the first video game ever- pong.
It is expected that all games have at least one or two in them but it has not been proven true on every single game so far. They are most common in First Person Shooter games and least common in arcade games. Not all of them are discreet either.
Here are a few examples of Ghost in the System: The Ghost of Lockout/Blackout myth in halo, Teleporting Sniper in Battlefield, Ghost Car in pretty much every racing game ever- there are two examples of this, one being when there's a car nobody seems to be driving in the game, the other where there's an invisible car in the game.
All Out War. It seems plain and simple but it actually.....ok it is simple. It originated on the website Neopets.com when some roleplayer wanted to have a roleplay and just fight his damn ass off but nobody in the roleplay forums joined. The next day he went to the Evil things and monster sightings forums and posted it and it turned out to be a huge hit there instead.
Nobody remembers who created it or when it was made though, it's just always been there, like herpes. It probably isn't going on today still but if you find it is then join it, it's really cool. You can fight somebody, watch a fight, intervene in a fight, practice throwing virtual knives, that kinda thing, or just hang out or lurk.
dude: hey man, wanna roleplay?
man: no thanks dude, i'm meeting slayer on AOW.