At the end of a financial year, you may have an outstanding tax liability. You can claim the tax credit reflected in your Form 26AS.
After claiming all the deductions and tax credit, you may still have tax dues. In this case, you will be required to pay the tax dues before filing ITR. It is also called self-assessment tax.
There are 2 modes to pay tax dues:
You will not be able to file ITR unless you pay these tax dues.