Bit depth
The number of steps available for each colour channel; more bits mean smoother gradations.
Also: colour depth, 8-bit, 10-bit
Digital colour is stored as whole numbers. Bit depth says how many are available. With 8 bits per channel, each of red, green and blue has 256 levels, about 16.7 million colours in all. That is enough for most pictures, but in very smooth areas, such as a clear sky, the steps can become visible as bands. With 10 bits there are 1,024 levels per channel, and with 16 bits over 65,000. Higher depths are used for HDR video and for editing photographs, where heavy adjustments would otherwise cause stepping.