dust jacket; book jacket; dust cover
Refers to the removable paper cover of a book, often used for protection or decoration. Wasei-eigo from English 'book cover', but in English 'book cover' usually means the permanent cover, while ブックカバー specifically means the dust jacket.
wasei-eigo (Japanese-coined English), from book cover
The library books have dust jackets on them.
This dust jacket has a lovely design, doesn't it?