OA Of Register: When two sheet passes on a press are misaligned.

OBC: Outside back cover.

Oblong: A term used to describe printed books, catalogs etc., that are bound on their shorter side; also referred to as album bound.

OFC: Outside front cover.

Off-shore Paper: Any papers made outside the US and Canada.

Offset: The most commonly used printing method, whereby the printed material does not receive the ink directly from the printing plate but from an intermediary cylinder called a blanket which receives the ink from the plate and transfers it to the paper.

Offset Gravure: A complex offset process involving multiple transfers between the gravure plate, the plate cylinder and a solid rubber plate.

Offset Lithography: Indirect printing method in which the inked image on the press-plate is first printed onto a rubber blanket, then in turn offsets the inked impression on to the sheet of paper.

Offset Paper: A term for uncoated book paper.

Onionskin: A light bond paper used for typing and used with carbon paper because of its thinness.

Opacity: Quality of papers that defines its opaqueness or ability to prevent two-sided printing from showing through.

Opaque: A quality of paper that allows relatively little light to pass through.

Opaque Ink: Ink that completely covers any ink under itself.

Orthochromatic: Any light sensitive surfaces that are not sensitive to red.

Over Run: Surplus of copies printed.

Overhang Cover: A cover of a book that extends over the trimmed signatures it contains.

Overlay: A transparent sheet placed over artwork, in register with the work it covers; this is used to call out other color components of the work, instructions or corrections.

Overlay Proof: A process of proof making whereby the color separations are individually exposed to light sensitive film. This film is then set in registration with a piece of white paper in the background.

Overprinting: Any printing that is done on an area that has already been printed.

Overset: Type that is set in excess of the allotted space.