Social dining is when someone goes out for dinner (generally with a group, or to meet up with a group) in the early hours of the evening (between 4:00pm and 6:00pm), and don't come home until late that night or early the next morning (between 10:00pm and 1:00am). This is referred to as social dining because it is not possible to spend that much time eating, and the social aspect causes the extended time period. Sometimes social dining involves going to multiple restaurants.
I'm babysitting from 4:00 to 11:00 tonight. The parents must be going social dining.
We're going out social dining tonight, so we'll be home late.