That's not what we're talking about. This has nothing to do with a Wiki website like that.
A Wiki post is usually the second post in a thread and anyone can edit it. It's a Wiki for the thread only.
Here's an example. The 2nd post of this thread is a Wiki post. In this case, people are using it keep track of rebate forms for some offer. Usually it's used to keep track of the most pertinent info on the thread. It keeps people from asking the same questions over and over:
http://forums.slickdeals.net/showthr...11248&t=987539
I can think of several cases where a Wiki thread would help. For example, there were very long threads on the NW MilesToGo promo and the Delta 25-Partner promo.