It's a tiny low latency aptX Bluetooth transmitter (compatible with any audio source with 3.5mm aux port). We added it here for your convenience on airplanes so you can make the in-flight entertainment totally wire free. You plug it into the 3.5mm aux port (usually on the armrest or next to the TV on the back of the seat in front of you), and then it will transmit audio stream to your BTunes. Note, you can pair it with other Bluetooth devices too.