This is the ALSA device name of your player. You have a few options here.
Default - this will select the default Audio device on your system.
hw:X,X - this will select the audio device with that device number and port number.
An exmaple device is hw:0,0 this is usually the default audio device on your system.
You can use the information listed at the bottom of this page to select the device number and port number for your device.