Lines per inch or LPI refers to the number of dot lines created per inch, which provides an indication of image sharpness. The finer the "screen" used to create printing plates, the more detail can be portrayed in the final printed piece. Most color printing is performed between 133 and 175 lines per inch.
The spatial resolution of a device, photographic emulsion, and so forth, expressed as the greatest number of parallel lines per inch that can be resolved. Related only indirectly to dots per inch, which specifies addressing resolution, but not the greatest number of lines that can be sensed or created, which will be at least two times smaller.