MKS BT is a board that contains the hardware of the hc06 chipsets.
This is a bt adapter that is used on some reprap ramps and MKS Gen with bt connection
print over Bluetooth
In order get rid of the USB connection between RAMPS or MKS Gen and the PC one may like to use Bluetooth.
You can connect MKS BT on AUX-1, and the default baut is 9600. You can change it Melzi
Connect RAMPS 1.4
Connect MKS GEN