In large scale RPG games (mainly LARPs and online tabletop games running 24/7), plot that specifically focuses on a given character and may or may not come out of nowhere or unexpectedly from the residing Storytellers or their assistants. This can happen to more than one character at a given time and at different time periods based on the progress and effect. It can also be a known plot line that is progressively happening in a given game. This term is used by the players and not their characters in-game.
The Plot bus just hit me last night! I found out my character's a sleeper double agent from the enemy!