quarto
A book in which the sheets have been folded twice,
the second fold at right angles to the first. The
result is often squarer than the upright
rectangular characteristic of the FOLIO , OCTAVO , and DUODECIMO . In books
with laid paper the chain lines are horizontal. In
England the quarto became an elegant format for
published works in the first half of the 18th
century.
In the 19th century, when the rapid mechanization
of the printing industry took place, librarians
began to apply the term format according to size
rather than the way a book was put together. This
has contributed considerably to the general
confusion concerning format.