Generally holiday is used to talk about the Christmas/New Year time off from work and other celebrated religious days of the year. For example: How were your holidays? What are you doing over the Christmas holidays? Happy holidays! When we look at the calendar and see all the days marked for certain celebration we call these holidays. For example: There are 2 (or however many) holiday days in the month of February. Usually these are the days the government has designated as manditory days off from work and so they usually are scheduled for a Monday so people can have a long weekend. So we might say: What are you doing for the holiday weekend. We use vacation for the specific time period chosen for a break off of work. Example: I have 2 weeks vacation coming up. In the school year to talk about scheduled time off, other than holiday weekends, we can also say: Christmas break, Spring break and when school is finished Summer vacation.
It's been a little while since I've been in the English community and I could be missing a few examples. I hope others will add to mine for you.
Hope this helps a bit.