3.5mm stereo audio jack, Low profile
A 3.5mm stereo jack socket for PCB mounting. Good for adding stereo audio output to MP3 player projects.
You must be wondering why there are 5 pins in the socket. When plug is not inserted, the pins 2-3 and 4-5 are connected. When plug is inserted they are disconnected. Typically used in stopping signal to go to other parts where muting is required and instead signal are routed to plug instead. You must have seen in some units that when headphone plug is inserted the amplifier speaker is muted.