It could really be any of those, but here in Bangkok they usually call it an anime convention.A convention is a meeting of a group with a similar interest, viewpoint or hobby. I've never heard of them being called "expos" as this has a more commercial feel to it, in my view. "Fair" makes me think the focus is more on small shops and selling things, especially outdoors, rather than dressing up.

We usually call those Cosplay Conventions (If I´m understanding you correctly!). Look up Cosplay and that might help you.