As their names imply, they have a different purpose. Bluetooth transmitter is connected to a non-Bluetooth audio source (CD player, TV, mp3 player, etc.) and it transmits/sends the audio signal to a Bluetooth-enabled sound output device (Bluetooth headphones, Bluetooth speaker). Bluetooth receivers, on the other hand, are connected to a non-Bluetooth sound output device and they receive the Bluetooth audio signal sent from a Bluetooth-enabled audio source.