Nozzle pitch.

Nozzle pitch is the centre-to-centre spacing between nozzles across the width of a printhead, and it is what sets the head's native resolution, published as native dpi or as nozzles per inch. The catch is that few heads put every nozzle in one row: rows are staggered or overlapped, so native dpi is the reciprocal of the effective spacing once all rows are projected onto a single line, not of the gap between two nozzles sitting side by side. Some heads also publish a lower figure for a redundant mode, where the array covers each addressed position more than once so a blocked nozzle does not leave a white line, and on a scanning machine anything finer than the array comes from interlacing extra passes rather than from the head. Quote a job at a resolution the array never had and the soft type shows up on a proof the customer already signed, which makes it your reprint.