Books bound in a format that uses thick, sturdy, relatively stiff binding boards and a cover composed (usually) of cloth spine and finished binding paper. Hardcover books are conventionally wrapped in a dust jacket. ( see: binding, dust jacket)
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.