Acoustic coupler

In telecommunications, the term acoustic coupler has the following meanings:

1. An interface device for coupling electrical signals by acoustical means--usually into and out of a telephone instrument.

2. A terminal device used to link data terminals and radio sets with the telephone network.

Note: The link is achieved through acoustic (sound) signals rather than through direct electrical connection.

Source: from Federal Standard 1037C and from MIL-STD-188