So what exactly is a TED book? I'd say that the above screenshot sums it up nicely. The ebooks are shorter than a novel and yet longer than a typical magazine article, and they are inspired by the talks given at TED conferences. They average around 15 to 20 thousand words, which is just long enough for a single idea to be explored fully.
This video should tell you more:
TED currently has around fifteen titles in print, and for now most of the titles in the iPad app will be enhanced versions of their backlist. The iPad app (apps for other platforms like Android are in the works) is a free download and like the Kindle iPad app the TED Books app is both an ebookstore and a reader. Books are sold for $3, but you can also get a recurring 3 month subscription for $15. Those that sign up in the first 90 days will also get free access to the entire back catalog of TED Books.
Now the app itself is rather interesting. It's clearly based on The Atavist app, which was an excellent choice. The TED Books app takes advantage of most (all?) of The Atavist's current features, including embedded photos, video, and audio, as well as footnotes, links, and embedded timelines. Each ebook will also come with the conference talk which inspired it.
But one detail that bothers me, and this is why I don't like format proliferation, is that I don't see a way for previously bought ebooks (via Kindle, Nook, or iBooks) to be accessed via the app. If you want the extras you'll have to buy the ebook a second time.