For display, gradation is a color progression expressing gradual changes in the depth of color shades.
In a nutshell, gradation refers to the passing of one color tint or shade to another, from the lightest to the darkest. Low gradation has a limited range of colors than can be expressed, thus it may cause aliasing on the image and undermine detailed color reproduction. On the other hand, abundant gradation expressions can reproduce more natural images.
In the display industry, gradation refers to the gradual changes of colors arranged in linear order using the differences in lightness.
In simple terms, it means the level of color expressions changing progressively from the lightest to the darkest.
The more shades a gradation spectrum has, the richer and more detailed colors a display can express.