skin book
/ˈskɪn bʊk/noun
1A book made of parchment or vellum, especially one containing literary works from medieval Iceland or Scandinavia.
2 Slang. A pornographic book or magazine; a cheap paperback with erotic subject matter.
Origin
Early 19th century; earliest use found in The Times. From skin + book. In later use of sense 1 after Icelandic skinnbók or Danish skindbog; compare Old Icelandic skinna.