Oh, heck, it's 2 in the morning and I'm fading fast, but I'll do what I can for ya....
When Disneyland opened in 1955 you had to buy individual tickets to go on each ride. The cheapest, smallest rides were A Tickets and they cost a dime. The middle tier rides were B Tickets, and the "big rides" on Disneyland's opening day like Jungle Cruise and the Mark Twain were C Tickets. In 1956 Walt opened the Mine Train Through Nature's Wonderland and it was even fancier than the Jungle Cruise and so the D Ticket was introduced. A through D Tickets existed through 1958. Then, in June 1959 a big expansion of Disneyland opened with the debut of the Matterhorn Bobsleds, the Submarine Voyage, and the Disneyland Monorail. All three of these rides were bigger and more lavish than anything prior, and the famous E Ticket was introduced and neccesary for gaining admission to the three new rides. All three of those rides still exist at Disneyland today, although they have been dramatically improved and changed over the last 49 years. They are all definitely still E Tickets!
From 1959 onward the E Ticket was the top tier admission ticket to the biggest and best rides at Disneyland. The term "E Ticket" entered the American lexicon in the 1960's because of it, meaning something really good. When Walt Disney World opened in 1971 they used the same ticketing setup as Disneyland, and the E Tickets at the Magic Kingdom were the big fancy rides like the Haunted Mansion, the Submarine Voyage, It's A Small World, etc.
When Epcot opened in 1982 the individual ride tickets were phased out at Disney parks in favor of an all-inclusive "passport". By the mid 1980's the individual tickets disappeared on both coasts, and only passports were used to enter the park and then allow you to ride as many rides as you could as many times as you wanted. No tickets required.
But the term "E Ticket" remains, and is used to indicated an attraction that is the fanciest, most thrilling, or most elaborate ride at a Disney theme park. :wave: