I often find myself in a situation where I need to explain to a non-tech person what Wikidot is. And I do not have an hour for long talk, just a sentence or two. The shorter the better. And it's perfect when people respond That's interesting, I need to try it.
One thing for sure, there is such an enormous diversity among sites on Wikidot that it might seem difficult to find a definition what Wikidot really is. I could say "Wikidot is a platform that empowers its users to build amazing wikis", which is very close to truth.
A problem I find is that many people have no idea what a wiki is. Those who do, when they say wiki, they often mean Wikipedia. You can use this fact by saying Do you know Wikipedia, the largest online encyclopedia that people collaboratively edit? So Wikidot is like "a small Wikipedia for everyone". But this does not really work. One look at most popular Wikidot sites and you will see they are nothing like "small Wikipedias".