Hairline
A very thin line or gap about the width of a hair or 1/100 inch. 

Halftone
Using small dots to produce the impression of a continuous-tone image. The effect is achieved by varying the dot size and the number of dots per square inch. Light areas have small dots and darker areas or shadows have larger dots.

Halo Effect
Faint shadow sometimes surrounding halftone dots printed. Also called halation. The halo itself is also called a fringe.

Hanging Punctuation
Punctuation that is allowed to fall outside the margins instead of staying within the measure of the text.

Head Margin
That space which lies between the top of the printed copy and the trimmed edge.

Head-to-Tail
Imposition with heads (tops) of pages facing tails (bottoms) of other pages.

Hickey
The effect that occurs when a spec of dust or debris (frequently dried ink) adheres to the printing plate and creates a spot or imperfection in the printing.

High Bulk Paper
Paper stock that is comparatively thick in relation to its basis weight.

High Key Halftone
A halftone that is made utilizing only the highlight tones down through the middle tones.

Highlight Dot
The highest density of a halftone image.

Highlights
The lightest tones of a photo, printed halftone or illustration. In the finished halftone, these highlights are represented by the finest dots.

Hinged Cover
Perfect bound cover scored 1/8 inch (3mm) from the spine so it folds at the hinge instead of along the edge of the spine.

Hollow
That space on the spine of a case bound book between the block of the book and the case binding.

Hot Melt
An adhesive used in the binding process, which requires heat for application.

House Sheet
Paper that is normally kept in stock in-house.