I'd give that a try. Others feel free to chime in.
Meeting - hold by a meeting facilitator (usually owner of the topic) with defined meeting agenda and process. Target to come out with a decision or a status update.
Conference - large in scale (several thousands) lasting for a day or more with multiple training topics/sessions. Usually kicking off with 1 or a couple key-note speech(es). If you have a corp mktg team, this is part of the Event Mktg team ownership.
Symposium - usually is a bit more interactive with audience participating in the discussion. Topic could be open and easy for a wider audience to paricipate or even present.
Seminar - usually referring to training course on a relatively serious topic, theory or methodology, sort of accademic focus. There is a instructor/trainer for the class.
In my environment, we have something call Brown Bag, not sure if this is close.
Brown Bag - a loosely organized meeting/training/discussion on a topic with 1 or multiple domain experts, sharing findings and best practices on a topic. Usually done over lunch time with a rather lay back environment, no registration required and people will come and go as they wish.