DNF

Did Not Finish - used often in the bookish community to signify books that were never completed by the reader, often because of a loss of interest, a disliking for the book, or another reason. DNFed books are usually books that the reader doesn't intend to return to, but sometimes the book is completed many months or years later.

"Did you ever finish that book I let you borrow?"
"Sorry man, it was a definite DNF for me."

"What about that book that you got for Christmas?"
"It's a DNF for sure, it was incredibly boring."