By 
A social interview is when they take you out for lunch or dinner, invite you to attend a social event or company conference, or take you to a professional association meeting. There are actually two purposes for this type of interview.
The first purpose is to get to know you in a more informal way to determine if you really fit in well with the team. In today’s increasingly team-based work environment, team compatibility is critical to success. Remember, they already know you can get the job done, now they are determining if you will be a productive member of the team.
The second purpose is to see how you perform in a social setting, especially if you will be interacting with clients or prospects in public. It’s presentation (how you behave), networking, and manners (yes, Mom was right, they are important).
Understand that this is not a break from the interview process, but part of it. Getting it right may not earn you big points, but doing it wrong can hurt you irreparably.
Some advices:
o You are not there for the food.
oDon’t eat anything dirty or leaky (or if you MUST make sure it matches your suit so it doesn’t show too much).
o Take care of your table manners (my mother was never so critical)
o Think about the way you would work the table at a business lunch and double it: don’t dominate, include everyone, be unfailingly polite.
oSometimes it is not so clearly part of the interview process. If you are invited to a company event or something similar, the same rules apply – this is an interview, not a social event. Be outgoing but be on your guard.