French flap

plural French flaps

1. pluralA publishing format of a paperback book with folded flyleaves, or either of the two flyleaves so folded.

   That same text also appeared in a “couture inspired” jacket, complete with deckle edges and French flaps to use as bookmarks.

   2013 February 13, Janine Barchas, The New York Times

   1 more example

   The one format no one ever forgets is known as "French flaps", a paperback edition with folded flyleafs. It is attractive, but so expensive it is almost never approved.

   2005 February 13, Nicholas Blincoe, The Telegraph