Dai Pai Dong are local restaurants where the tables are outside in the open-air.
It seems that there aren’t that many left in Hong Kong and they get quite busy, especially at dinner time.
From a foreigner point of view, these little restaurants can look quite dodgy, but I’ve been to two different (relatively clean) ones and didn’t have any tummy issues.
Atmosphere is really relaxed with family/friends gathering for rowdy dinners and waiters swearing happily.
Dai Pai Dong are really part of the local culture and nice thing to try at least once while in Hong Kong.