When
Disneyland first opened you paid for admission and a book of tickets. There were A tickets, B tickets, etc. Each attraction was given a rating (A thru E) and you used the corresponding ticket to go on the ride. E tickets were the premier rides (today they would be Splash Mtn., Space Mtn., California Screamin', etc.) When you were out of E tickets you were out of chances to ride those rides - although presumably you could buy more ticket books. I don't know when Disney stopped using the tickets - I know they were still in use during my first trip in about 1973. Anyway, the premier rides are still sometimes referred to as E-ticket rides - rides that would have taken an E ticket if they were still being used.