ZFT
ZFT is a top-secret book located in the Dark Magic wing of the Royal Library of Canterlot. It was among the books Sunset Shimmer either read, or was to read.
![](http://static.miraheze.org/mylittleponywiki/thumb/6/6b/ANNUAL2013_Books_left.png/400px-ANNUAL2013_Books_left.png)
Behind the scenes
It's possible that "ZFT" may be a reference to "Zerstörung durch Fortschritte der Technologie", often shortened to "ZFT", a terrorist organization from Fringe.