Yeh it is the tfn declaration form. It asks u for your tfn, some personal details and then some information about superannuation, deductions and whether you want to claim any benefits e.g. the tax-free threshold and stuff like thatdoe said:maybe they mean a tax file number declaration form?
if you dont have a tax file number (TFN) you get one from the ato. if you dont declare it you get taxed at the highest rate.