A tax file number (TFN) is a unique nine-digit number that identifies taxpayer for tax and superannuation (super) purposes.
TFN is an important part of tax and super records as well as a taxpayer identity, so need to be kept secure.
Only one TFN is issued by ATO during taxpayer’s lifetime so once a taxpayer is issued a TFN , he doesn’t t need to apply for a new one. Taxpayer will keep the same TFN even if its circumstances changes like for individuals even if they change their name, change jobs, move interstate or go overseas, TFN will remain the same.
A taxpayer can work without a TFN but more tax will be deducted payments being made to him and for individuals on super contributions. Taxpayer will also not be able to lodge tax return electronically, apply for Government benefits or get an Australian business number (ABN).
You can have more information on Tax File Number from ATO website by clicking here