I ran into this issue when telling people about Bay Hac. In college, at least, "hackathon" has acquired a pretty specific meaning: a *competitive* coding marathon, often with prizes. Bay Hac, on the other hand, was really more like a mini-conference: talks, sessions and lots of socializing, but no competitive aspect at all. (Personally, I like this quite a bit more than a normal hackathon!) I didn't want to send the wrong impression, but I also didn't know what else to call it except for "hackathon".
Even though BayHac had *some* aspects of a hackathon, I still don't think it's a great description. If focuses on the wrong aspects. In my view, the most important parts of BayHac were educational and social, and it was incredibly valuable even if you didn't finish or even work on a project. This is pretty much the opposite of most actual hackathons I see; even when they have some focus on education, they still tend to be heavily "getting-things-done" project oriented.
I'm really not sure what the best noun to use is, but I'm leaning towards describing it as a mini convention or conference.