Monochrome is for pics that are primarily one color.
Grayscale is for pics that are primarily in shades of gray. (nobody uses this tag)
Grayscale -> monochrome, but monochrome does not necessarily mean grayscale. i.e. >>402182
Black-and-white is the same as grayscale. I assume black and white is also used for something else, too. Like a tv show or video game or something. But we’re never that consistent with tagging.
Lineart is for line art? I’m not an artist or willing to pretend I know dick about art, so I don’t know how this differs from sketches and such.
Grayscale and black-and-white are literally the same thing. Black is just the strongest intensity of gray, while white is the weakest (or is it the other way? whatever). I haven’t axed black and white as a tag yet because I assume it’s used for different contexts.