This is what Disney e-mailed me. I was trying to figure it out too. I hope that this helps.
Lori
Non-Peak Season:
January 2 through mid-February (excluding holiday weekends)
The week following Labor Day until the day before Thanksgiving
The week after Thanksgiving until the week prior to Christmas
Moderate:
After Presidents' Day week in February through early March
Late April through early June (with the exception of Memorial Day
weekend)
The week leading up to Thanksgiving Day
Peak Season:
Presidents' week in February
Mid March through Late April (Spring Break period)
Memorial Day weekend
Mid June through Labor Day (Summer Season)
Veterans' Day
Thanksgiving Day and the following weekend
December 25 through January 1