Sometimes a useful way to define what something is… is to define what it is not. This is the principle behind the amusing, frustrating and frequently-cited Wikipedia policy "What Wikipedia is not".

Its necessity comes from the fact that simply stating "Wikipedia is an encyclopedia" isn't enough to tell you what that means in practice. While the "Britannica model" was its starting point, because Wikipedia is digital, bound by neither page count nor publishing deadline, it does far more than Britannica ever could.

But this doesn't mean anything goes, and finding the outline of Wikipedia's mission is challenging. By subtracting potential features the community has determined Wikipedia should avoid, we can look at the negative space around Wikipedia to find its true shape.

So, what isn't Wikipedia? A dictionary, soapbox, directory, crystal ball and more. Over the next few weeks, we'll examine a few and discuss why—that is, why not.