What is sensor?
Sensors are devices which sense or detects a physical property and provide that data as an input to other devices or record or respond to it. We can say sensors are electronic devices that take input from outer environment and provide that data as an output to other electronic devices.
The term “input device” in the definition of a Sensor means that it is part of a bigger system which provides input to a main control system (like a Processor or a Microcontroller).