3.5mm TRS Male

A 3.5mm TRS Male connector is a type of electrical connector primarily found on consumer electronic level devices.  It is commonly not thought of as a professional level input or output (think old school consumer level iphone headphone ending).  A TRS cable has a tip, a ring, and a sleeve (usually two black lines), whereas a TS cable only has a tip and a sleeve (only one line). 

3.5mm TRS Male connectors are typically used for sizing down a 1/4 in TRS adaptor to fit into a consumer electronic device.  Often times, you will see 3.5mm TRS male adaptors then split into a left & right mono cables terminating in various endings like RCA and 1/4 TS.  A 3.5mm TRS Male connector, while a balanced connector, is normally used to handle stereo signals rather than balanced mono signals.  This is exactly what your consumer level headphones are doing with that 3.5mm TRS connector at the end. It's there to transmit stereo sound to your headphones with one side holding the Left signal, and the other side holding the Right signal.