Palenque,
If you are referring to the word "used" in the topic of this thread, it's referred to as people who have bought these tickets new and then used them at the parks. When you order from these ticket dealers, you will be getting brand new tickets. An actual used ticket would have no days left or just a few, but not as many as you originally bought the ticket with (example: a 5 day pass with three days left is used) these tickets will never expire and you can hold on to passes with remaining days for future visits