Bit depth is maximal number of value digital signal measurement.
Distinguish audio and video bit depth.
Sound (oscillations of air) at each instant has different values.
Intensity of air pressure to ear changed in time.
The stronger the pressure changes, the louder the sound.
We have analog (uninterrupted) signal (air pressure).
Converting analog signal to digital format
Measurements of the value (of the air pressure power) at the each instant stored into memory.
By time the instants are spaced equally.
Bit depth audio is maximal value of the measurement (pressure).
Bit depth may be integer or floating point number.
Integer bit depth consists some number bits (8, 12, 16, 20 ,24, 32, 64).
More number of bits less level (loudness) of noise (more precision of the measurements).
Floating point bit depth has range 0.0 ... 1.0
1.0 is highest level of air pressure.
For different purposes used various bit depths:
Speech, lo-fi music - 8 bit
Hi-Fi, Hi-End CD, DVD-video, downloaded audio - 16 bit
Hi-Fi, Hi-End DVD-audio and video, Blue-Ray, downloaded audio - 24 bit
Studio recording and mixing (music production) - 24 or 32 bit and 32 or 64 bit float
For high precision applications - 64 bit integer or floating point
Each pixel (point of monitor or TV screen) has 3 colours.
Each colour has level of brightness 0 to <bit-depth>.