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Paperback - *en.wikipedia.org/wiki/Paperback
Paperback, softback, or softcover describe and refer to a book by the nature of its binding. The covers of such books are usually made of paper or cardboard, and are usually held together with glue rather than stitches or staples.
Hardcover - *en.wikipedia.org/wiki/Hardcover
A hardcover (or hardback or hardbound) is a book bound with rigid protective covers (typically of cardboard covered with cloth, heavy paper, or sometimes leather). They may have flexible sewn spines which allow the book to lie flat on a surface when opened, although most modern commercial hardcover books have glued spines.