Essentially a transducer is an electronic device which converts energy from one form to another. Some examples you may be familiar with include microphones and loudspeakers. There are two different types of transducer an input transducer which is a sensor and an output transducer which is an actuator.

What is the purpose of a transducer?

A transducer converts some sort of energy to sound (source) or converts sound energy (receiver) to an electrical signal.

Is transducer a sensor?

Both a sensor and a transducer are used to sense a change within the environment they are surrounded by or an object they are attached to, but, a sensor will give an output in the same format and a transducer will convert the measurement into an electrical signal.