To start discussion on What are Digital systems? we should know that electronics systems are in two types’ analog electronics and digital electronics. Now question is what are Analog electronics and Digital electronics?
Analog electronics deals with things that are continuous in nature and digital electronics deals with things that are discrete in nature. But both are interconnected to each other’s. Now take an example 
which is elaborate whole thing with ease, suppose we press a switch and a bulb is grown and when we press that switch in reverse position then light is off. Now think on that process in term of switch then it must digital system because when switch is on light grown and switch off light off. It has only two state on (logic 1) and off (logic0). But if we think the above mention system regarding light then it is analog .Because when we press the switch that time the AC current with specified voltage and frequency is reached to bulb through wire.
Now think, many of us use electronic amplifiers. And think what an amplifier does? It amplifies electronic signals. Generally those signals usually have a continuous in nature and hence can take up any value within a given range, and are known as analog signals.
But in case of digital system there has only two states logic high or logic low(i,e 1,0) The signal must always be in either of the two levels. As long as the signal is within a specified range of HIGH and LOW, the actual value of the signal is not that important. Those signals are called digital signals and the circuit used to make a complete the system is called a digital circuit and the complete system is called a digital system.
Now days we are used digital system in our daily life. It used in communication, business transactions, traffic control, spacecraft guidance, medical treatment, weather monitoring, the Internet, and many other commercial, industrial, and scientific enterprises.
