A measure of resolution, or the number of "dots"—be they screen pixels or printer spots—that comprise an image. Lines per inch, in this sense, is somewhat synonymous with pixels per inch or dots per inch; since lines are composed of pixels and dots, the number of lines in an inch will equal the number of dots per inch. The greater the number of lines—or dots—per inch, the greater the resolution and the sharper the image.
In halftone generation, halftone screens are measured in lines per inch, which is equivalent to the number of halftone dots per linear inch. Thus, a screen described as 150-line would contain 150 rows and 150 columns of dots, or 22,500 dots per inch.