According to the FT glossary "DO" is: "A widely used term for large get togethers/parties/meetups. In general the term is reserved for larger gatherings of 12 of more members."

According the FT rules: "A gathering of FlyerTalk members, often referred to as a "Do," is to be posted in the CommunityBuzz Forum, but the main thread may be in a different forum and then cross referenced to CommunityBuzz. Members may not be excluded from events announced on FlyerTalk based on factors such as gender, age, number of posts or location."

DOs may range from a meal in a local restaurant to a few days of organized activities attracting members from all over the world. There are also regular DOs (usually meals) in several locations round the world. Take a look at the Consolidated Do List Thread which has links to the past DOs as well as upcoming DOs to find what FT DOs are like and how they are organized. I personally believe planning, announcing, discussing and reporting of DOs is what the CommunityBuzz forum is for rather than just a place for announcing gatherings/meetups.