Symposium vs. Conference and Congress

[Adelaide9216]

What's the difference between all three? 

[fuzzylogician]

Depends on the field, I don't think there is a general answer. I'd think of a conference as something that has a CFP where anyone can submit, and (if accepted) present their work. A symposium would be organized and speakers might only be by invitation. It'd be much smaller than a conference (though there are also small conferences). A symposium would always be organized around a theme; a conference might, but doesn't have to, and the theme would be broader. My field doesn't have anything like a "congress" so I'm guessing here, but it sounds like it could be the largest of the three.. so maybe like a large conference with a much broader appeal. But again, I actually don't know what you mean by that. 

[AP]

I've only seen the word 'Congress' in large, mostly international conferences. I cannot think of a small conference being a congress.