Answer:
shades of grey
Step-by-step explanation:
A grey scale image contains various shades of grey, ranging from white to black... and the number of the shades present in the image depends on the number of 'colors'.
A grey scale photo for example is what we usually call a black and white photo, since it only has black, white and everything in between those two basic colors.
Besides photography, pure grey scale images are rarely used because it could be difficult to see the difference between two shades, while it's much easier when using colors.