So, this is leaving me thinking about what gatherings of people I've been to that I think qualify as a "convention", and why.
I went to one gathering that was pretty clearly a smallish convention. A whole bunch of people in a hotel for a weekend, using hotel function space, playing a variety of different games.
I went to another gathering that was of the same form as the convention, but much smaller - the whole thing fit in one person's home. Do I want to count that?
I went to a third thing that was roughly the same size as the second, but took up hotel rooms and function space, but we were all playing the same game. And I don't mean like a Magic or chess tournament, full of separate instances of play of the same game. I mean, like, all of us playing in the giant instance of play. Do I want to count that?
So, somewhere between one and three?