Stafford Loan discharge: Stafford Loan Discharge and Cancellation

TPD is for if you are dying of your disability; it is literally total/permanent (such that you would not be able to go back to school, even if you "wanted" to). You have to be certified that you have been totally disabled for 5 years (60 months) or will not be doing better for at least 5 years (presumably because you're going to die before then), etc. The loan gets discharged because it is assumed you are not going to be doing anything much but dying and might need the money/to wrap up your affairs, etc.

https://studentaid.ed.gov/repay-loan...lity-discharge