With binary I meant 1-bit pixels; in mspaint.exe this is called monochrome bitmap. I find the distinction convenient because one dimensional color can be called grayscale or black and white. Maybe 1-bit could be called black or white.

The term doesn't originate with computers, so the mono in monochrome doesn't refer to the 1 bit, but to the one colour. One dimensional colour isn't necessarily grey so monochrome is only greyscale when referring to black and white images.

If you make a cyanotype print of a black and white image the colours are blue, white and all the blue shades in between. One colour, but it's not greyscale.

Fair enough. Anecdotally though I've gone to the printer's and had problems expressing the binary/1-bit color conceptualization.