from Fancyclopedia 2 ca. 1959
Is applied to the back cover of magazines, not books. In the proz they're full of Carnu ads or plugs for the Linguaphone Institute — and sometimes ads for magic, trusses, canopeners and gas-saving gadgets — but in fanzines are often decorated with cartoons, poems, and Eavesdroppings. In its current incarnation this practice seems to have been begun by Art Rapp, who added to Spacewarp's bacovers poems addressed to the postmen who delivered that illustrious mag.