Never been offered one, but from what I understand/have read for people staying in an onsite resort during a certain time frame, they would leave a card in your room offering you another vacation at a discounted rate to be used during a certain time frame.
For example. You're staying at Pop in November and they are trying to fill rooms in April. They might offer you a 2nd (bounceback) vacation during April at a cheaper rate.
Hope this helps.
~Karen