Bit depth

Bit depth tells you how many bits are used to represent a value. In display color, you will often see bits per component or bits per sample: the precision of one color component. An 8-bit component has 256 possible integer values; a 10-bit component has 1024. Bits per pixel can include several components and additional storage, so it is a different quantity. Apple’s bitmap-format explanation

More precision allows finer steps between tones. It does not, on its own, give a display a wider color gamut, enable HDR or tell you the physical precision of its panel.

BetterDisplay's Color Depth and Color Mode menus expose different choices supplied by the system. Their meaning and availability depend on the platform and display. See Color Depth for its options and Resolution for the separate question of desktop size.