I wouldn't say it is a festival or a seminar but more of a gathering.
A gathering of fellow members discussing and planning new initiatives. A chance to meet the people who you have been talking to over the last year. Finding new people and making proper acquaintances and life long friendships.
We are all like minded people with a common interest in Steem. To meet others in a informal environment for 3 or 4 days is something that we at some point would all like to do. There will be announcements with new initiatives and the knowledge and understanding shared will be invaluable.
Having the chance to meet new people and grow your followers by actually knowing them would be an advantage.
It is a large gathering put on by @roelandp if memory serves me right and it is not adtually anything put on by steemit its self. It consists of a lot of seminars and is a time for developers to pimp their product in order to try and garner support/ delegations/ investors.