Which is correct?

Question

1. What did you do for the winter vacation?
2. What did you do for winter vacation?

I think #2 is correct, if so ( or not ) how do I back this up with a specific rule?

Answer 1

#2 is the better of the two, yes.

http://grammar.ccc.commnet.edu/grammar/determiners/determiners.htm
Here is an excellent webpage from a college in Connecticut that explains the uses of articles in English.