If your application does not use *any* board level drivers, you can ommit the definition of the BOARD macro. However, some users may wish to write their own custom board hardware drivers which are to remain compatible with the LUFA hardware API. To do this, the BOARD macro should be defined to the value BOARD_USER. This indicates that the board level drivers should be located in a folder named "Board" located inside the application's folder.
When used, the driver stub files located in the DriverStubs folder should be copied to the user Board directory, and fleshed out to include the values and code needed to control the custom board hardware. Once done, the existing LUFA board level APIs (accessed in the regular LUFA/Drivers/Board/ folder) will redirect to the user board drivers, maintaining code compatibility and allowing for a different board to be selected through the project makefile with no code changes.