In digital electronics, there are only two possible values—ON or OFF. In real life, we can not describe everything as ON or OFF. Many entities can have a wide range of values. For example, weight cannot be described as ON or OFF. You need to specify a number to describe magnitude of weight. Weight can be 66 kg. It can be 65.9 kg. It can be 65.93472641 kg. All these are valid numbers to describe weight. The possible values for analog entities are infinite, unlike with digital systems. The same holds true for analog entities like length, temperature, air pressure, and so on. If we plot a graph of values over time, we get an analog signal wave. The disadvantage of analog information is it's susceptible to noise and information is lost during transmission due to distortion, non-linearities, and so on.
Most of the sensors are of analog type. They get information from the environment. Often the information is a unit or a scalar value of the environmental entity. Then they convert that...