small fandom? or not so small?

I was wondering: by what criteria is a fandom a "small fandom"? Is it by the number of fanworks one can find of it? And if that's the case, do you use a single site, or more than one?

Let me explain why I'm curious: I'm currently re-reading the Artemis Fowl series, since I hadn't read the last book, and I wanted to refresh my brain on what happened before. I decide to look for fanfiction of the series. AO3 has 193 works. Compared to other fandoms I read on that site, that's not a lot.

However, is it a "small fandom"? Another site would beg to differ.

I occasionally go to fanfiction dot net in an attempt to find stories that AO3 doesn't have a lot of. The fanfic count for Artemis Fowl: 4.7K. 4700~. That is definitely not a small number.

I really am curious, especially since I'm thinking (only thinking, not sure if I actually will) of signing up this year's Yuletide exchange.

Please tell me: what defines a "small fandom"?