Hairline register: Printing registration that lies within the range of plus or minus one half row of dots. It is the thinnest of the standard printers' rules.
Halftone: Tone graduated image composed of varying sized dots or lines, with equidistant centers.
Halftone Paper: A high finish paper that is ideal for halftone printing.
Halftone Screen: A sheet of film or glass containing ruled right-angled lines, used to translate the full tone of a photo to the halftone dot image required for printing.
Hard Dot: The effect in a photograph where a dot has such a small degree of halation that the dot shows quite sharp.
Head Margin: That space which lies between the top of the printed copy and the trimmed edge.
Hickies: Imperfections in presswork due to dirt on press, trapping errors, etc.
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.
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: This is a term that refers to a paper that a printer keeps on hand in his shop.