Definition: Quite simply, this means a black-and-white image. Literally, it is the range of neutral shades of gray spanning from white to black. The term is typically used when editing photos on software (where you can convert a color digital image to a black-and-white photo) and in printing (where you can choose to print color pages as grayscale only to conserve color inks).
Examples: That photo I took of the old building might look better in grayscale.