Weird looking speaker?

Fullmetal A

New member
I took apart an old broken cellphone, and inside was a speaker with 4 wires on it. the 4 wires are Yellow black red and blue. the red and blue are connected to terminals labeled spk + and spk - and i know what those are. however, the black and yellow are connected to terminals labeled RCV + and RCV -. what does the RCV stand for.
 
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