One-eighteenth of a sheet. The eighteen-mo is an
unusual method of imposition resulting in a
section of 18 leaves, or 36 pages. One method of
producing it is to fold a sheet concertina-wise,
followed by an envelope fold, followed by a right
angle fold. Although used in book production
between about 1770 and 1840, it is seldom, if
ever, used in bookwork today. It is, however,
sometimes used in advertising work, etc., where
the folded sheet is to be untrimmed and remain
folded in compact form until unfolded for reading.
Also written 18mo. Also called "octodecimo."