Everything in the real world is analog it has an infinite resolution limited only by the tools we use to measure it.
Everything on the computer is digital and we only have a finite amount of storage and memory.
When we want to store things from the real world on computers we cannot store all of this detail. We try our best to represent the real world on computers but it’s only a “sample” of what’s there in real life.
To store anything from the real world onto a computer we have to use a ADC (Analog to Digital Converter). When using a ADC we are taking these samples of the real world, and the digital quality of the data captured is dependent upon the resolution of the ADC.