The _SFR_WORD() is a macro that returns two bytes of data of the specified address.

The _SFR_WORD() is defined in hardware/tools/avr/avr/include/avr/sfr_defs.h as below.

#define _SFR_WORD(sfr) _MMIO_WORD(_SFR_ADDR(sfr))

It returns a macro that returns two bytes of data of the specified address. The _SFR_ADDR() is a macro that returns the address and the _MMIO_WORD() is a macro that returns two bytes of data of the specified address.