What is Hydrophone?

Hydrophone definition and meaning on Dictionary terms:
a device for locating sources of sound under water, as for detecting submarines by the noise of their engines.
an instrument employing the principles of the microphone, used to detect the flow of water through a pipe.
Medicine/Medical. an instrument used in auscultation, whereby sounds are intensified through a column of water.


reference: https://www.dictionary.com/browse/hydrophone