Publishers often create a blad as a form of pre-publication sales material for upcoming books. Blad stands for book (or, basic) layout and design. Dictionary.com suggests that the word comes from bl(urb) + ad. It is sometimes written in all caps as BLAD.
A blad is a booklet, often wire-bound, consisting of a few sample pages or chapters of a book with a proof of the front and back covers or book jacket. It serves as a preview of the book for promotional use, reviewers, and advance sales.
A blad is similar to a galley although the galley is typically a low-cost version of the entire publication sent out to book reviewers, rather than just a sample.
Unrelated to publishing, blad is also a slang term for a friend, derived from blood (See the Urban Dictionary)