Printing Glossary – Terms starting with O

Offset	An erroneous variation of the word “setoff”. Ink that is unintentionally transferred from a printed sheet to the back of the sheet above it as the pieces are stacked in a pile when printed.
Offset paper	A term for sometimes used for uncoated book paper.
Offset printing	The most commonly used printing method, where the printed material does not receive ink directly from a printing plate but from an intermediary blanket that receives the ink from the plate and then transfers it to the paper.
Onion Skin	A specific lightweight type (kind) of paper usually used in the past for air mail. Seldom used today (in the typewriter era)
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	(1) Not transparent. (2) To cover flaws in negative with tape or opaquing paint. Also called block out and spot
Opaque ink	Ink that completely covers any ink under itself.
Open Prepress Interface	Hardware and software that link desktop publishing systems with color electronic prepress systems
Outer form	Form (side of a press sheet) containing images for the first and last pages of the folded signature (its outside pages) as compared to inner form
Outline Halftone	Halftone in which background has been removed or replaced to isolate or silhouette the main image. Also called knockout halftone and silhouette halftone
Over Run	Additional printed matter beyond order. Overage policy varies in the printing industry. Advance questions avoid blind knowledge
Overlay	Layer of material taped to a mechanical, photo or proof. Acetate overlays are used to separate colors by having some type or art on them instead of on the mounting board. Tissue overlays are used to carry instructions about the underlying copy and to protect the base art
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.
Overprint	To print one image over a previously printed image, such as printing type over a screen tint. Also called surprint
Overprinting	Any printing that is done on an area that has already been printed.
Overrun	Quantities of sheets printed over the requested number of copies.