The books on the centre and left are hardback books
A hardback, hardcover, or hardbound book is one with stiff covers.
The covers are of rigid cardboard. They are usually covered with cloth or heavy paper. A heavy cloth like buckram, or a leather is sometimes chosen.
It should have a flexible, sewn spine which allows the book to lie flat on a surface when opened. Less good is a glued spine, because the glue gets worse with time.
Hardback books may be printed on acid-free paper. They are much more durable than paperbacks. Paperbacks are often printed on cheap recycled paper, and have flexible, easily damaged paper covers. Hardback books are only slightly more costly to make, but are often much more expensive to buy.
Hardbacks may have artistic dust jackets, or designs printed right on the board binding.
Images for kids
Detail of "Twenty Thousand Leagues Under the Sea", first English edition (1873), showing cloth pattern on cover
A typical hardcover book (1899), showing the wear signs of a cloth cover over the hard paperboards
Dust jacket on a hardcover book
A Bible bound in blue leather
Hardbound book with half leather binding (spine and corners) and marbled boards.
Contemporary hardcover, with partial cloth cover, on the spine only, and boards for the rest