Also see Analog to Digital Conversion
An n-bit digital to analog converter with range, $b (volts)$ to $a (volts)$, the resolution is described with the following relation: $$ Res = \frac{b-a}{2^N} $$
On data sheets, the "resolution" refers to the number of bits used to perform the conversion.
An example is performed below.
In [1]:
b = +10 # +10 Volts
a = -10 # -10 Volts
N = 16 # 16 bit resolution
Res = (b-a)/2**N
print('Resolution =', Res, 'Volts/bit')