A double elephant folio is a book printed on double elephant paper, which measures 40 inches by 26.75 inches. The paper can be up to 50 inches long.
Based on five minutes of intensive internet research, the most famous double elephant folio appears to be Birds of America by John James Audubon, who wanted the birds in his book to appear life-sized. This blogger wonders what the book would have looked like if Audubon had been into insects instead.
I learned this from:
1. The Order of Things: Hierarchies, Structures, and Pecking Orders
2. What is a Double Elephant?
3. Book Sizes
P.S. The largest book on record is Bhutan: A Visual Odyssey Across the Last Himalayan Kingdom, which is five by seven feet and weighs 150 pounds. It costs $15,000 to get your own copy, but you can see photos of it at this link.
