FSR0 is a constant that equates to 0.
It's for use with the LFSR opcode, LFSR FSR0, 38

The address for the FSR0 is 2 bytes, FSR0L and FSR0H.
So with your example, it could be one of these ...
Code:
	LFSR  FSR0, 38
	
	MOVLW	57
	MOVWF	38
	MOVFF	INDF0,TXREG
... OR ...
Code:
	MOVLW	38
	MOVWF	FSR0L
	CLRF	FSR0H
	
	MOVLW	57
	MOVWF	38
	MOVFF	INDF0,TXREG
hth,