It means "The Rook on the f-file moves to d1 to give check".
In board positions where more than one piece of the same colour can move to a destination square the file letter or rank number is used to differentiate.
In your position, had white played the other rook to check the black king the notation would be Rad1+
Hello,
I want to know what is 'f' in "Rfd1+" .
I know the "Rd1+" but "Rfd1+" i don't know exactly what is it.
I think but not sure that 'f' means that "Rook" left Row 'f'.
Thanks.