Metaplot
Metaplot is a common strategy by a role-playing gaming company to reset canon.
In RPGs, the gamer is in charge. Acts of avatar heroism improve or at least alter the environment. The base environment, assuming the DM is lazy, gets bought from a gaming company like Games Workshop. This "fluff" sets out the world and its backstory.
Well, what if Games Workshop needs more dough. They'll put out a new edition, obviously. Which changes the rules, sometimes for the better (TSR 2e -> WotC 3e is a good example) but either way - changed.
With metaplot, the company invents some world-changing event and kicks up the calendar a few years. This gets sold as "Advancing the Storyline".
The reason /tg/ hates metaplot is that it takes the power from Your Dudes; you know, the actual storyline in a role playing game. Metaplot is a high-handed move by the company and, if not done well, looks like a naked cash grab. One egregious example is Arcana Evolved's restoration of the dragons to overhaul Arcana Unearthed which basically killed it.
Some companies at least try to involve the players. Some examples here: the Greyhawk Wars leading to From the Ashes, Die Vecna Die! leading to Third Edition across at least three settings, Hellbound: The Blood War taking the fiends' teleport away. Such campaigns have a foreordained conclusion, so tend to the railroad. There's also the issue that it sticks players into a specific year in the timeline; you cannot play Rise of the Runelords in the Golarion of Shattered Star. But if designed right, the players can make a difference around the edges.
Retcon is that specie of metaplotting which, by the laws of thermodynamics, cannot involve the players. That has its own page.
There are also milder, and thus much less hated, versions of "metaplot"; usually, it's a case of some subtext and interaction between books in a line that the player or reader need not care about, but is still there. For example, a nod to a previous book that only amounts to a brief cameo that makes a lot more sense if you've read the other book, but isn't necessary for understanding of this book nor particularly distracting. (e.g., the elf who wrote the in-universe fluff from the elf splatbook has a brief cameo in the dwarf splatbook.) In other words, the "it's there if you want metaplot, but it's not required in any way if you hate metaplot" compromise.
Metaplot Hall of Shame
Some metaplots are more disliked than others. Here is a list that people commonly complain about. [1]
- Warhammer Fantasy to Age of Sigmar
- (Old) World of Darkness, particularly in the shift between editions.
- Vampire, in particular, although Mage had it's bad bits of metaplot as well.
- Shadowrun
- The Spellplague