belles-lettres (n.)

"elegant literature, literature as fine art," 1710, French, literally "fine letters," from belles, plural of belle, fem. of beau "fine, beautiful" (see beau) + lettres, plural of lettre "letter" (see letter (n.)). The literary equivalent of beaux arts; its boundaries never have been exact, and it is "now generally applied (when used at all) to the lighter branches of literature, or the æsthetics of literary study" [OED].