Stereo 3.5mm Jack (headphone jack) to Stereo 3.5mm jack. Usually used to connect a headphone out to another jack input (e.g. audio in on a PC/AUX input on car). Used quite often in connecting PC s audio out/speaker out to the speakers on the side of monitors or to AUX input in a car. Short 15cm long 3.5mm Stereo Jack to 3.5mm Stereo Jack