the express pass that is for sale allows the person to use the express lane one time only for each ride and attraction.
if you go to the universal website, you can read more info about it.
if you are interested in buying it, wait and see if you need it. if you are in the parks and there are no crowds, it would be a waste of money.
there are no refunds for the express pass.
and, it is good only for the park you buy it for and on that date only.
if you stay on site at one of the three hotels, you get, as a perk, the express pass priviledges unlimited for the days and check out day you stay on site.