This one make me feel old!
When Walt Disney World first opened, long before Epcot and the other parks, when you paid park admission, you got a book of tickets. Each booklet had so many A tickets, B tickets, and so on. It took an E ticket to go on a major attraction, such as Space Mountain, Its a Small World, 20,000 Leagues under the Sea. (I'm trying to remember more, but there weren't that many major attractions in those days!) The lesser rides would be an lesser ticket--for example the carrousel was an A ticket.
When you used all your E tickets, there were booths in the park where you could buy additional tickets. As I recall, we always had a hard time using up the lesser value tickets, and always went home with extras. Somewhere in a scrapbook in the attic, I bet I could find a half a dozen A tickets right now!
It's a better system now for sure, but on the downside, I think park admission back then including the ticket booklet, was around $10.