Here is an article that goes into a little more depth. It looks like it is some kind of technology that is related to Google's method of providing books that aren't tied to a device.
I found a
link to a FAQ that describes their technology. It looks like it is an XML based alternative to ePub.
There are several other pages at which I haven't bothered looking. If you want to find them just go to Google and search for --
site:ebooktechnologies.com