For information from the ATO website click Special Disability Trusts - tax return lodgment instructions.
The SDT offset represents the credit for tax paid by a trustee to the beneficiary of a Special Disability Trust.
In previous years, this amount was claimed at Item 13 Share of credit for tax paid by trustee, label S. However, that was not optimal as label S credits are limited to gross tax payable.
Having recognised this shortcoming, the ATO has provided an area to claim back the tax paid by the Trustee for Section 98 estimates so that it is fully refundable.
Click label at T9 or press Alt+S to open the holding dialog and select the Special Disability Trusts offset worksheet.