Resolution refers to the number of bits used to represent an analog signal on an analog input device.
The higher the resolution which could make the voltage range to be divided finely, could convert the analog value more accurate to the digital value.
Devices with 12-bit resolution divide the range width by 4096. If the range of the device is 0 to 10V, the minimum unit of converted voltage will be 10 ÷ 4096 ≈ 2.44 mV. If the resolution of the device is 16-bit, the minimum unit of converted voltage will be 10 ÷ 65536 ≈ 0.153 mV.