It's Use Year. Let me try to explain. For every 12 month (year) period
DVC members get an allotment of points to use to travel. We don't all get our points on January 1. They are staggered thoughout the year and can be February, March, April, June, August, September, October, or December. It's the "birthday" for your points. If you have an April Use Year, each year you can spend or bank your points from April 1-March 31. The Use Year also determines the deadlines for making your point banking decisions.
Use Year does not have any effect on when you make your reservations. That's governed by 11 months from check-out date for your Home Resort and 7 months from check-out date for all other resorts.
The only time Use Year may have an effect is if you have a reservation scheduled during the last two months of your Use Year and you have to cancel it during those last two months. The problem is that the points have to be used by the end of the Use Year and you have missed the banking deadlines and may have missed the chance to use them at a non-DVC option as well. It's not really something to be overly concerned about.
If you vacation the same time every year and expect to stick with that pattern for the foreseeable future, you can try to get a Use Year that is a month or two prior to your travel time. However, it's nothing to go nuts over.