The leaves of the book are untrimmed, with the top and fore-edge folds still intact
If something is unopened, it has not been opened yet. unopened bottles of olive oil The letter lay unopened in the travel firm's pigeonhole Catherine put all the envelopes aside unopened. an unopened package, letter etc has not been opened yet
"This means that the leaves of a book issued entirely untrimmed (and therefore having the folding of its component sections still intact at the top and fore-edges) have not been severed from their neighbours with the paper-knife It must not be confused, as it often is by philistines, with UNCUT "
That the leaves of a book issued entirely untrimmed (the folding of sections still intact at both top & fore edges) have not been subsequently cut open
the leaves of a book comprise sheets of paper which have been printed and then folded several times before being sewn When sewing is complete the edges of the folds are trimmed Pages are described as 'unopened' in the case of any trimming which has failed to reach the folds