A BigWikiFire is a slightly silly term used to describe what happens when a wiki gets so incredibly difficult to work with and incomprehensible to visitors that it is effectively a Members-Only club. If you've been there long enough, you know it, otherwise you're screwed.
At this point, because everyone gets so emotional about their content, the only course of action is to cause a BigWikiFire. The original wiki database is frozen and a new wiki database is founded.
This occured at the PortlandPatternRepository. However, it is not something that anybody really wanted to do. If care is not taken to keep a wiki managable and StrangerFriendly, it can end up being the only choice.