Grayscale printing.

In inkjet, grayscale has nothing to do with black and white. It describes a head that can place more than one drop volume on the same addressable spot, either by switching the drive waveform or by firing several sub-drops that merge before they land, so the printed dot comes in several sizes instead of one. A binary head has on and off, so tone comes only from how many dots the halftone puts in a given area; a grayscale head adds dot size to that, which buys smoother gradients at the same pass count and lets a single nozzle row carry fine type and a flooded solid in one job. The weak point is that the drop levels are only as even as the individual nozzles: sub-drop volume and velocity vary across a bar, which is why Xaar ties its per-nozzle waveform and voltage trimming directly to banding and color density variation. On the floor that reads as a gradient that steps instead of flowing, or a fill whose density changes where one head hands over to the next, and profiling will not rescue it because the profile was measured on a head state that has since drifted.