Nicks.—Hollows cast in the front of the lower part of the shank of a type, to show the compositor how to place it in his stick.
Octavo, or 8vo.—Eight pages to a form.
Octodecimo, or 18mo.—Eighteen pages to a form.
Odd page or folio.—The 1st, 3d, and all uneven-numbered pages.
Off.—Signifies that the pressman has worked off the form.
Offcut.—A portion of a sheet that is cut off before folding.
Off its feet.—When matter does not stand upright.
Open matter.—Matter widely leaded or containing numerous break-lines.
Out.—An omission marked in a proof by the reader.
Out of register.—When the pages do not back each other.