"In the online communities of projects such as Wikipedia, OpenStreetMap, and LocalWiki an edit-a-thon...is an organized event where editors edit and improve a specific topic or type of content, typically including basic editing training for new editors. They often involve meetups, but can be distributed as well."
So, an edit-a-thon is just a bunch of people getting together to improve on collectively written knowledge.
Our project is fairly open-ended. However, you should know the following: